C64 RAM locations for programmable characters

 

Taking the information from Jim Butterfield's interactive program we can determine a few optimal choices for configuring the location of video and character set memory.  They both need to be in the same 16K bank of the C64 memory, video memory needs to be accessible to the KERNAL, and some locations are off limits (offsets $1000-$1FFF within VIC-II 16K banks 0, 2) because the VIC-II only sees D000-DFFF ROM characters there.

Option 1: easiest, video $0400, chars $2000-$2FFF

Option 2: least BASIC free, video $8C00, chars $A000-$AFFF

Option 3: largest free, video $CC00, chars $F000-$FFFF

Option 4: single charset, video $C400, chars $C800-$CFFF

Thanks to Jim Butterfield's SCREENMAP 64 program, it prompts for you to choose between valid options, and then calculates the register and screen page values that you need to change(poke).  Shown above are details for the four options that seem best.  The first three allow for two full sets of characters.  The last one allows for a single character set, or one and a half character sets.

In addition to the steps shown, it may be necessary to install an NMI handler to keep the values set instead of reset to ROM defaults, and it will be necessary to load a font into the desired programable character set address range.

Options 3 and 4 are interesting because they both increase BASIC RAM by 1K more than normal by moving video screen memory elsewhere. Option 1 is the easiest to implement, so is perfect for getting started.

Notes:

1000-1FFF not available for VIC because maps to D000 ROM

5000-5FFF not available for VIC because maps to D000 ROM

9000-9FFF not available for VIC because maps to D000 ROM

D000-DFFF not available for VIC because maps to D000 ROM

C000-CFFF not recommended for prog. chars. because other RAM in that bank not usually available to KERNAL needed for video screen characters.   So if screen characters are there, only room for one set (2K) instead of two sets (4K)

Option 0 (Normal)

0400-07FF screen memory (1K) = 1024

0800-9FFF BASIC RAM (38K) 

C000-CFFF free (4K)

D000-DFFF character ROM banked under I/O

Option 1 (First 16K)

0400-07FF screen memory (1K) = 1024

0800-1FFF free (6K)

2000-2FFF prog. chars. (4K) = 8192

3000-9FFF BASIC RAM (28K)

4000-7FFF is smack dab in the middle of BASIC RAM, seems like a bad idea unless used with 6502 machine language or other assets around it, and not strictly BASIC.

Option 2 (Third 16K)

0400-8BFF BASIC RAM (34K)

8C00-8FFF screen memory (1K) = 35840

9000-9FFF free (4K)

A000-AFFF prog. chars in RAM bank under BASIC ROM = 40960

Option 3 (Fourth 16K)

0400-9FFF BASIC RAM (39K)

C000-CBFF free (3K)

CC00-CFFF screen memory (1K) = 52224

E000-EFFF = 57344 prog. chars in RAM bank under KERNAL ROM *or* F000-FFFF = 61440 *or* under CHAR ROM D000-DFFF = 53248

Option 4 (Fourth 16K)

0400-9FFF BASIC RAM (39K)

C000-C3FF free (1K) or half lowercase character set (no inverse characters)

C400-C7FF screen memory (1K) = 50176

C800-CFFF prog. chars (1 set, 2K only) = 51200

MLX II Listing for C64 Character Sets Editor

Shown with 80s theme colors (key: 6)

Back in the day we would enter program listings from magazines.  That's how we got new utility and game software on a monthly basis.  It was a fun activity in front of my Commodore Vic-20 on Saturdays.

For nostalgia, and retro vibes, you can repeat the process to get this character editor program.   It's online elsewhere and pointed to in this blog, but if you have an air gapped C64, you can enter directly.

Note: Floppy drive 8 is required for loading/saving fonts and theme configuration.  This program does not support tape drives or alternate floppy drives.  So be prepared with a floppy drive 8 such as 1541, 1571, 1581.

Please enter the hex listing below using Compute's Gazette MLX II which includes a ninth checksum byte at the end of each line.  MLX will stop you from continuing if the checksum doesn't match it's internal algorithm.

e.g. I test entered using 64 MLX from Compute's Gazette disk from November 1993 

start:  0801

finish: 24b8

0801:0b 18 0a 00 9e 36 31 35 43

0809:37 00 00 00 00 00 00 00 b4

(gap of zeros or unused, use STOP+RESTORE if get stuck)

1800:00 0b 18 0a 00 9e 36 31 ae

1808:35 37 00 00 00 20 17 1f 6e

1810:18 66 a6 18 6e b1 24 a9 68

1818:00 85 22 a9 08 85 23 20 45

1820:a3 20 ad 18 d0 29 f0 8d fb

1828:b3 24 09 04 8d b4 24 20 44

1830:97 21 20 2b 20 a5 2c c9 e4

1838:18 f0 36 a9 01 a2 18 85 5a

1840:2b 86 2c a9 00 85 fb 85 5b

1848:fd a9 08 85 fc a2 d0 86 d5

1850:fe a9 10 85 ff a0 00 78 bf

1858:20 63 1f b1 fd 91 fb c8 67

1860:d0 f9 e6 fc e6 fe c6 ff e4

1868:d0 f1 20 5c 1f 58 20 7c 5e

1870:1f a9 93 20 d2 ff a9 13 0c

1878:20 d2 ff 2c b1 24 30 44 f2

1880:a9 a1 a2 22 20 8e 1d a9 83

1888:30 a2 23 85 b4 86 b5 20 81

1890:9f 1d 20 cc 1e a9 30 85 26

1898:fd a9 08 85 ff a9 be a2 52

18a0:23 20 8e 1d a5 fd 20 d2 46

18a8:ff a9 b3 a2 23 20 8e 1d b7

18b0:a9 20 20 d2 ff 20 9f 1d cb

18b8:e6 fd c6 ff d0 df 20 db d6

18c0:20 20 9f 1d 20 e1 1e a9 3d

18c8:00 85 27 a9 00 85 28 a9 e9

18d0:38 a2 04 85 29 86 2a a2 f8

18d8:d8 85 b2 86 b3 18 a5 a2 81

18e0:69 04 85 a3 20 b9 1d a0 74

18e8:00 b1 29 85 a7 ad 18 d0 f7

18f0:29 fe c9 10 d0 05 a9 12 af

18f8:8d 18 d0 20 8b 1e 20 e4 0c

1900:ff f0 ea 48 20 bb 1e 68 e4

1908:c9 4e d0 19 20 17 1f a5 9f

1910:22 69 07 85 22 90 c6 e6 ae

1918:23 a5 23 c9 10 90 be a9 30

1920:08 85 23 d0 b8 c9 2b d0 3d

1928:19 20 17 1f a5 22 69 7f cb

1930:85 22 90 a9 e6 23 a5 23 8c

1938:c9 10 90 a1 a9 08 85 23 1b

1940:d0 9b c9 42 d0 1a 20 17 65

1948:1f a5 22 e9 08 85 22 b0 a1

1950:8c c6 23 a5 23 c9 08 b0 3a

1958:84 a9 0f 85 23 4c dd 18 8f

1960:c9 2d d0 1a 20 17 1f a5 bf

1968:22 e9 80 85 22 b0 0c c6 41

1970:23 a5 23 c9 08 b0 04 a9 53

1978:0f 85 23 4c dd 18 c9 11 b0

1980:d0 31 a5 29 69 27 85 29 ca

1988:85 b2 90 05 e6 2a e6 b3 ed

1990:18 a5 28 69 01 29 07 85 14

1998:28 d0 15 38 a5 29 e9 40 1f

19a0:85 29 85 b2 a5 2a e9 01 66

19a8:85 2a a5 b3 e9 01 85 b3 2a

19b0:4c e7 18 c9 91 d0 33 a5 7e

19b8:29 e9 28 85 29 85 b2 b0 cc

19c0:05 c6 2a c6 b3 38 a5 28 ca

19c8:e9 01 29 07 85 28 c9 07 2d

19d0:d0 15 18 a5 29 69 40 85 03

19d8:29 85 b2 a5 2a 69 01 85 30

19e0:2a a5 b3 69 01 85 b3 4c 70

19e8:e7 18 c9 1d d0 1e e6 29 16

19f0:e6 b2 a5 27 69 00 85 27 e7

19f8:29 07 d0 0d 38 a5 29 e9 01

1a00:08 85 29 85 b2 a9 00 85 d8

1a08:27 4c e7 18 c9 9d d0 18 df

1a10:c6 29 c6 b2 c6 27 10 0d f5

1a18:18 a5 29 69 08 85 29 85 ab

1a20:b2 a9 07 85 27 4c e7 18 a3

1a28:c9 13 d0 17 a9 00 85 27 11

1a30:85 28 a9 38 85 29 85 b2 78

1a38:a9 04 85 2a a9 d8 85 b3 05

1a40:4c e7 18 c9 20 d0 11 20 ba

1a48:1e 1f a6 27 a4 28 b1 22 e5

1a50:5d 91 22 91 22 4c dd 18 0b

1a58:c9 03 d0 1b 20 f1 21 ad b6

1a60:b5 24 8d 18 d0 18 4e b1 e0

1a68:24 a9 d4 a2 23 20 8e 1d b1

1a70:20 cc 1e 20 e1 1e 60 c9 bf

1a78:53 d0 49 20 80 20 a9 93 21

1a80:20 d2 ff a9 0a 85 39 a9 96

1a88:00 85 3a a9 c0 85 9d a9 01

1a90:01 a2 08 a0 0f 20 ba ff 67

1a98:a9 0b a2 d6 a0 23 20 bd b5

1aa0:ff a9 00 85 fb a9 08 85 b3

1aa8:fc a9 fb a2 00 a0 18 20 42

1ab0:d8 ff a9 ec a2 23 20 8e c5

1ab8:1d 20 e4 ff f0 fb 20 96 6e

1ac0:20 4c 71 18 c9 93 d0 0f 15

1ac8:20 1e 1f a9 00 a0 07 91 35

1ad0:22 88 10 fb 4c dd 18 c9 cd

1ad8:12 d0 11 20 1e 1f a0 07 24

1ae0:b1 22 49 ff 91 22 88 10 d5

1ae8:f7 4c dd 18 c9 3c d0 10 5a

1af0:20 1e 1f a0 07 b1 22 0a f7

1af8:91 22 88 10 f8 4c dd 18 5d

1b00:c9 3e d0 10 20 1e 1f a0 1e

1b08:07 b1 22 4a 91 22 88 10 4d

1b10:f8 4c dd 18 c9 d6 d0 16 74

1b18:20 1e 1f a0 07 88 b1 22 b3

1b20:c8 91 22 88 10 f7 c8 a9 87

1b28:00 91 22 4c dd 18 c9 5e 0d

1b30:d0 18 20 1e 1f a2 07 a0 ec

1b38:00 c8 b1 22 88 91 22 c8 90

1b40:ca d0 f6 a9 00 91 22 4c 60

1b48:dd 18 c9 46 d0 25 20 1e 8a

1b50:1f a0 03 84 ff c8 84 fe 12

1b58:a4 ff b1 22 48 a4 fe b1 bd

1b60:22 aa 68 91 22 a4 ff 8a a6

1b68:91 22 e6 fe c6 ff 10 e8 fb

1b70:4c dd 18 c9 52 d0 25 20 24

1b78:1e 1f a0 00 a2 00 b1 22 34

1b80:0a 91 22 76 a8 e8 e0 08 7e

1b88:d0 f4 c8 c0 08 d0 ed a0 89

1b90:07 b9 a8 00 91 22 88 10 04

1b98:f8 4c dd 18 c9 4d d0 26 e6

1ba0:20 1e 1f a0 07 a2 07 b1 de

1ba8:22 4a 91 22 b9 a8 00 2a 71

1bb0:99 a8 00 ca 10 f1 88 10 f3

1bb8:ec a0 07 b9 a8 00 91 22 94

1bc0:88 10 f8 4c dd 18 c9 40 46

1bc8:d0 14 ad b5 24 cd b4 24 63

1bd0:f0 06 20 74 20 4c ed 18 72

1bd8:20 62 20 4c ed 18 c9 2a 0e

1be0:d0 2d ad aa 24 ae ad 24 86

1be8:ac af 24 8e aa 24 8c ad 7b

1bf0:24 8d af 24 ad a9 24 ae df

1bf8:ac 24 ac ae 24 8e a9 24 e1

1c00:8c ac 24 8d ae 24 20 a3 f0

1c08:20 20 cc 20 4c dd 18 c9 c7

1c10:5a d0 24 a6 a4 f0 1d a5 61

1c18:a5 d0 07 20 1e 1f c6 a4 d9

1c20:a6 a4 e6 a5 ca 86 a4 8a 50

1c28:20 4c 1f a0 07 b1 fb 91 f9

1c30:22 88 10 f9 4c dd 18 c9 11

1c38:43 d0 0f a0 07 b1 22 99 0f

1c40:51 02 88 10 f8 84 a6 4c 27

1c48:ed 18 c9 56 d0 14 24 a6 e1

1c50:10 0d 20 1e 1f a0 07 b9 fc

1c58:51 02 91 22 88 10 f8 4c d0

1c60:dd 18 c9 58 d0 16 20 1e 89

1c68:1f a0 07 b1 22 99 51 02 70

1c70:a9 00 91 22 88 10 f4 84 c4

1c78:a6 4c dd 18 c9 59 d0 0d b6

1c80:a5 a5 f0 09 c6 a5 e6 a4 e2

1c88:a6 a4 4c 27 1c c9 2f d0 70

1c90:32 20 17 1f a9 00 a2 08 59

1c98:85 fb 86 fc a2 10 85 fd 91

1ca0:86 fe a2 08 86 ff a0 00 26

1ca8:b1 fb aa b1 fd 91 fb 8a e1

1cb0:91 fd c8 d0 f3 e6 fc e6 73

1cb8:fe c6 ff d0 eb 20 7c 1f 27

1cc0:4c dd 18 c9 85 d0 16 ee c0

1cc8:86 02 ad 86 02 4d 21 d0 3b

1cd0:29 0f f0 f3 20 cc 1e 20 4f

1cd8:b9 1d 4c ed 18 c9 89 d0 69

1ce0:1b 18 ad a8 24 69 01 29 de

1ce8:0f 8d a8 24 ad 21 d0 4d 44

1cf0:a8 24 29 0f f0 eb 20 b9 cd

1cf8:1d 4c ed 18 c9 86 d0 10 2c

1d00:ee 21 d0 ad 21 d0 4d 86 5c

1d08:02 29 0f f0 f3 4c ed 18 43

1d10:c9 8a d0 10 ce 21 d0 ad 37

1d18:21 d0 4d 86 02 29 0f f0 ec

1d20:f3 4c ed 18 c9 87 d0 06 ba

1d28:ee 20 d0 4c ed 18 c9 8b af

1d30:d0 06 ce 20 d0 4c 38 1d 75

1d38:c9 88 d0 1b 18 ad a7 24 30

1d40:69 01 29 0f 8d a7 24 ad 86

1d48:21 d0 4d a7 24 29 0f f0 40

1d50:eb 20 b9 1d 4c ed 18 c9 a5

1d58:8c d0 11 18 ad a6 24 69 6a

1d60:01 29 0f 8d a6 24 20 b9 df

1d68:1d 4c ed 18 c9 48 d0 0b 9f

1d70:ad b1 24 49 80 8d b1 24 c8

1d78:4c 71 18 c9 30 90 0c c9 7a

1d80:3a b0 08 29 0f 20 eb 20 88

1d88:4c 76 18 4c ed 18 85 fb 25

1d90:86 fc a0 00 b1 fb f0 06 c6

1d98:20 d2 ff c8 d0 f6 60 a9 f0

1da0:cf a2 23 20 8e 1d a5 b4 ba

1da8:a6 b5 20 8e 1d c8 98 18 e5

1db0:65 b4 85 b4 90 02 e6 b5 d6

1db8:60 a9 38 a2 04 85 24 86 c3

1dc0:25 a2 d8 85 b0 86 b1 a9 56

1dc8:08 85 ff a0 00 a2 08 b1 be

1dd0:22 85 26 ad a6 24 91 b0 b6

1dd8:ad a9 24 06 26 90 08 ad 6a

1de0:a7 24 91 b0 ad aa 24 91 27

1de8:24 e6 24 e6 b0 d0 04 e6 99

1df0:25 e6 b1 ca d0 dd 18 a5 2e

1df8:24 69 1f 85 24 85 b0 90 05

1e00:04 e6 25 e6 b1 c8 c6 ff 49

1e08:d0 c3 2c b1 24 10 03 4c f1

1e10:e1 1e 20 6c 1f a2 19 86 cb

1e18:24 86 b0 a2 04 86 25 a2 6f

1e20:d8 86 b1 38 66 ff a0 00 98

1e28:20 65 1e e6 24 e6 b0 d0 ee

1e30:04 e6 25 e6 b1 18 66 ff f5

1e38:a2 08 18 a5 24 69 25 85 bb

1e40:24 85 b0 90 04 e6 25 e6 fb

1e48:b1 ad ab 24 2c b0 24 30 1d

1e50:02 a9 e5 91 24 e6 24 d0 a3

1e58:02 e6 25 b1 22 20 65 1e 89

1e60:c8 ca d0 d6 60 48 4a 4a 3e

1e68:4a 4a 20 7a 1e e6 24 e6 c3

1e70:b0 d0 04 e6 25 e6 b1 68 b8

1e78:29 0f 09 30 c9 3a 90 02 8b

1e80:e9 39 24 ff 10 02 09 80 9f

1e88:91 24 60 38 a5 a3 c5 a2 10

1e90:d0 28 a5 a2 69 1d 85 a3 8c

1e98:a0 00 ad a7 24 2c b0 24 ac

1ea0:10 0c b1 29 49 80 91 29 49

1ea8:ad a8 24 91 b2 60 b1 b2 b0

1eb0:29 0f cd a8 24 d0 f1 20 f1

1eb8:b4 20 60 a0 00 a5 a7 91 e4

1ec0:29 20 b4 20 18 a5 a2 69 38

1ec8:02 85 a3 60 a0 00 ad 86 c8

1ed0:02 99 00 d8 99 00 d9 99 1c

1ed8:00 da 99 00 db c8 d0 f1 94

1ee0:60 a9 b8 a2 05 85 fb 86 b5

1ee8:fc 2c b1 24 10 10 a0 00 29

1ef0:a9 20 91 fb c8 d0 fb 20 9d

1ef8:6c 1f a8 91 fb 60 20 0e 11

1f00:1f 2c b1 24 30 10 a9 d0 37

1f08:a2 06 85 fb 86 fc a0 00 f2

1f10:98 91 fb c8 d0 fa 60 a9 e7

1f18:00 85 a4 85 a5 60 a5 a4 43

1f20:c9 18 90 15 a2 00 a0 08 0b

1f28:b9 3c 03 9d 3c 03 e8 c8 15

1f30:c0 c4 d0 f4 a2 17 86 a4 8c

1f38:8a 20 4c 1f a0 07 b1 22 e5

1f40:91 fb 88 10 f9 e6 a4 c8 d5

1f48:84 a5 18 60 0a 0a 0a 18 df

1f50:69 3c 85 fb a2 03 90 01 06

1f58:e8 86 fc 60 a5 01 09 07 9c

1f60:85 01 60 a5 01 29 f8 09 af

1f68:03 85 01 60 a5 23 85 ff 74

1f70:a5 22 46 ff 6a 46 ff 6a a9

1f78:46 ff 6a 60 a9 00 a2 10 cf

1f80:85 fb 86 fc a2 38 85 fd 20

1f88:86 fe a2 08 86 ff a0 00 14

1f90:b1 fb 91 fd c8 d0 f9 e6 1d

1f98:fc e6 fe c6 ff d0 f1 60 e2

1fa0:2c 19 d0 30 03 4c 31 ea ee

1fa8:ad 19 d0 29 01 f0 f6 ad 18

1fb0:b2 24 10 2a ad 12 d0 c9 17

1fb8:c2 90 f9 a2 0a ca d0 fd 01

1fc0:ad b6 24 8d 18 d0 a9 00 38

1fc8:8d 12 d0 8d b2 24 ad 11 d7

1fd0:d0 29 7f 8d 11 d0 a9 01 aa

1fd8:8d 19 d0 4c 25 20 f0 2a b8

1fe0:ad 12 d0 c9 8a 90 f9 a2 5e

1fe8:0a ca d0 fd ad b5 24 8d f2

1ff0:18 d0 a9 a4 8d 12 d0 8d d2

1ff8:b2 24 ad 11 d0 29 7f 8d 18

2000:11 d0 a9 01 8d 19 d0 4c 01

2008:25 20 ad b4 24 8d 18 d0 3c

2010:a9 68 8d 12 d0 8d b2 24 58

2018:ad 11 d0 29 7f 8d 11 d0 45

2020:a9 01 8d 19 d0 68 a8 68 9a

2028:aa 68 40 78 a9 00 8d b2 82

2030:24 a9 00 8d 12 d0 ad 11 06

2038:d0 29 7f 8d 11 d0 ad 14 2f

2040:03 ae 15 03 e0 1f f0 10 f5

2048:8d a6 1f 8e a7 1f a9 a0 73

2050:a2 1f 8d 14 03 8e 15 03 1c

2058:ad 1a d0 09 01 8d 1a d0 e3

2060:58 60 ad b4 24 29 f0 09 96

2068:02 8d b5 24 29 f0 09 0e 33

2070:8d b6 24 60 ad b4 24 8d c5

2078:b5 24 09 02 8d b6 24 60 cd

2080:ad b5 24 8d b7 24 ad b6 c2

2088:24 8d b8 24 ad b4 24 8d ad

2090:b5 24 8d b6 24 60 ad b7 87

2098:24 8d b5 24 ad b8 24 8d 6d

20a0:b6 24 60 a9 80 8d b0 24 ab

20a8:ad aa 24 cd a9 24 d0 03 4e

20b0:4e b0 24 60 a4 28 b1 22 1a

20b8:a6 27 3d 91 22 c9 01 ad be

20c0:a6 24 90 03 ad a7 24 a0 94

20c8:00 91 b2 60 a9 24 a2 23 10

20d0:20 8e 1d 20 db 20 a9 92 af

20d8:4c d2 ff a9 ee a2 22 2c 01

20e0:b0 24 30 04 a9 09 a2 23 a2

20e8:4c 8e 1d c9 00 d0 02 a9 24

20f0:0a c9 0b 90 01 60 a8 a9 97

20f8:49 a2 24 85 fb 86 fc 88 df

2100:f0 0f 18 a5 fb 69 09 85 f8

2108:fb a5 fc 69 00 85 fc d0 c8

2110:ee a0 00 b1 fb 8d 86 02 32

2118:c8 b1 fb 8d 21 d0 c8 b1 13

2120:fb 8d 20 d0 c8 b1 fb 8d 67

2128:a6 24 c8 b1 fb 8d a7 24 84

2130:c8 b1 fb 8d a8 24 c8 b1 b4

2138:fb 8d a9 24 c8 b1 fb 8d e5

2140:aa 24 c8 b1 fb 8d ab 24 a6

2148:20 a3 20 20 cc 1e 4c 51 52

2150:21 ad aa 24 c9 a0 d0 13 ab

2158:a9 20 8d ac 24 a9 2a 8d 9d

2160:ad 24 a9 cf 8d ae 24 8d b1

2168:af 24 60 c9 2a d0 13 a9 98

2170:cf 8d ac 24 8d ad 24 a9 ea

2178:20 8d ae 24 a9 a0 8d af e0

2180:24 60 a9 20 8d ac 24 a9 35

2188:a0 8d ad 24 a9 20 8d ae 0e

2190:24 a9 2a 8d af 24 60 a9 e5

2198:fe a2 23 20 8e 1d 20 6d ff

21a0:22 d0 4d a9 0a 85 39 a9 ee

21a8:00 85 3a a9 c0 85 9d a9 2f

21b0:01 a2 08 a0 00 20 ba ff 1d

21b8:a9 08 a2 e4 a0 23 20 bd 04

21c0:ff a9 00 a2 b9 a0 24 20 50

21c8:d5 ff a2 09 a0 00 b9 b9 0d

21d0:24 99 a3 24 c8 ca d0 f6 4c

21d8:ad a3 24 ae a4 24 ac a5 fe

21e0:24 8d 86 02 8e 21 d0 8c b0

21e8:20 d0 20 a3 20 20 51 21 f2

21f0:60 ad 86 02 29 0f 8d a3 04

21f8:24 ad 21 d0 29 0f 8d a4 2f

2200:24 ad 20 d0 29 0f 8d a5 19

2208:24 20 5c 22 f0 4d 20 80 91

2210:20 a9 1f a2 24 20 8e 1d b8

2218:20 6d 22 d0 3e a9 0a 85 4b

2220:39 a9 00 85 3a a9 c0 85 43

2228:9d a9 01 a2 08 a0 0f 20 f0

2230:ba ff a9 0b a2 e1 a0 23 b8

2238:20 bd ff a9 a3 85 fb a9 6b

2240:24 85 fc a9 fb a2 ac a0 96

2248:24 20 d8 ff a9 ec a2 23 2b

2250:20 8e 1d 20 e4 ff f0 fb f2

2258:20 96 20 60 a2 09 a0 00 d6

2260:b9 b9 24 d9 a3 24 d0 04 65

2268:c8 ca d0 f4 60 20 e4 ff 7a

2270:f0 fb c9 4e d0 0b a9 45 95

2278:a2 24 20 8e 1d a9 01 d0 66

2280:0f c9 59 f0 04 c9 0d d0 2b

2288:e4 a9 40 a2 24 20 8e 1d b7

2290:60 80 40 20 10 08 04 02 d9

2298:01 7f cf df ef f7 fc fd 8c

22a0:fe 0d 20 12 20 20 43 48 1d

22a8:36 34 45 44 49 54 20 20 fd

22b0:0d 20 12 20 20 28 43 29 19

22b8:20 32 30 32 34 20 20 0d 32

22c0:20 12 20 20 44 41 56 49 bc

22c8:44 20 52 2e 20 20 0d 20 20

22d0:12 20 56 41 4e 20 57 41 e7

22d8:47 4e 45 52 20 0d 20 12 a9

22e0:20 44 41 56 45 56 57 2e 34

22e8:43 4f 4d 20 0d 13 20 20 63

22f0:20 20 20 20 20 20 20 20 35

22f8:20 20 20 20 20 12 20 37 1c

2300:36 35 34 33 32 31 30 20 3f

2308:00 20 20 20 20 20 20 20 3e

2310:20 20 20 20 20 20 20 20 56

2318:12 20 a3 a3 a3 a3 a3 a3 b4

2320:a3 a3 20 00 13 92 11 11 3b

2328:11 11 11 11 11 11 11 00 5d

2330:0d 00 12 40 2d 2b 2a 2f dc

2338:59 5a 58 43 56 0d 00 12 f9

2340:42 92 41 43 4b 20 12 52 f9

2348:92 4f 54 41 54 45 0d 00 1c

2350:12 4e 92 45 58 54 20 12 40

2358:4d 92 49 52 52 4f 52 0d b9

2360:00 12 3c 3e 5e 56 92 20 28

2368:12 46 92 4c 49 50 0d 00 06

2370:12 46 31 92 2d 12 46 38 17

2378:92 20 12 30 2d 39 0d 00 bd

2380:12 48 4f 4d 45 92 20 12 67

2388:43 4c 52 0d 00 12 52 56 e1

2390:53 92 20 20 12 53 50 41 ea

2398:43 45 0d 00 12 53 54 4f 49

23a0:50 92 20 12 53 92 41 56 96

23a8:45 0d 00 12 48 92 49 44 59

23b0:45 0d 00 92 20 20 20 20 e7

23b8:20 20 20 20 12 00 1d 1d 05

23c0:1d 1d 1d 1d 1d 1d 1d 1d 07

23c8:1d 1d 1d 1d 1d 12 00 92 1e

23d0:20 20 20 00 93 00 40 30 80

23d8:3a 46 4f 4e 54 2e 42 49 c5

23e0:4e 40 30 3a 46 4f 4e 54 68

23e8:2e 43 46 47 0d 0d 12 50 65

23f0:52 45 53 53 20 41 4e 59 4d

23f8:20 4b 45 59 0d 00 93 0d fc

2400:4c 4f 41 44 20 43 4f 4e a9

2408:46 49 47 55 52 41 54 49 8d

2410:4f 4e 20 28 59 2f 4e 29 67

2418:3f 20 12 59 92 9d 00 93 7e

2420:0d 53 41 56 45 20 43 4f d1

2428:4e 46 49 47 55 52 41 54 91

2430:49 4f 4e 20 28 59 2f 4e 10

2438:29 3f 20 12 59 92 9d 00 5a

2440:59 45 53 0d 00 4e 4f 0d a6

2448:00 0e 06 0e 0e 00 01 20 48

2450:a0 a0 01 00 0f 00 01 0b b6

2458:cf cf a0 05 00 00 00 05 e5

2460:05 20 2a a0 06 01 03 0f cb

2468:00 03 cf cf a0 00 0b 0c 8f

2470:0f 00 0e cf cf a0 0d 06 20

2478:08 07 02 04 cf cf a0 0b 11

2480:00 08 0f 08 09 20 a0 a0 d7

2488:0d 0b 0d 0c 00 04 20 a0 6d

2490:a0 00 01 0e 0f 0e 05 cf b4

2498:cf a0 0e 00 00 00 0b 06 ce

24a0:20 a0 a0 00 00 00 0e 00 51

24a8:01 20 a0 a0 20 2a cf cf b0

24b0:80 00 00 10 14 12 1e 00 5f

24b8:00 00 00 00 00 00 00 00 01

Edit Programmable Characters on Vic-20 and C64

 

The current release is considered fully functional and complete.

Links:

Vic-20 D64 (1541 image) and source

Commodore 64 D64 (1541 image) and source

The Commodore Vic-20 video chip added multiple features beyond what the original PET Model 2001 offered.  Besides color support, it also includes the ability to change to user defined character sets.  These can be used to customize the look and feel of a program, and also to provide bitmapped graphics.

Back in the 80s I was proud of my development of a character editor program that utilized a few machine language routines to perform quick operations via keyboard selections.   Unfortunately I don't have direct access to that program today (haven't been able to read the tape back into the computer yet).  So I decided to rewrite it again.

This time it is purely 6502 assembly code.  I started using the VICE monitor to write the initial functionality, and soon afterwards transitioned to ACME source to ease edits and additions.

After mocking up the look of the screen, identifying operations that would be nice to have, and testing out memory layout and configuring the video chip to use character images from RAM, I got to work.

1. Initial screen layout including editor and commands.

2. Navigation of character selection, displaying bit patterns for editing to screen, and displaying hex character value and byte values.

3. Editing the pixels in a single character.

4. Saving font to floppy disk.

5. Continuing to iterate with new features and enhancements

Description of key operations

pressing a key on the keyboard as shown below will perform an operation:

@ - toggle between RAM/ROM character sets

SPACE - toggle pixel on/off

B - navigate back one character

C - copy

F - flip upside down

M - mirror the image left to right, right to left

N - navigate forward to next character

R - rotate 90 degress to the right

S - save to FONT.BIN (WARNING: overwrites any previous saves)

V - paste

X - cut

Y - redo

Z - undo

- minus - navigate 16 characters back

+ plus - navigate 16 characters forward

< > - shift pixels left/right

↑ - shift pixels up (^ carrat on PC)

Shift V - shift pixels down

CLR - erase all pixels

CURSOR keys - move cursor left/right/up/down

HOME - move cursor to upper left position

RVS - inverse the pixels

STOP - exit (usually mapped to ESC on PC)

There are up to 24 levels of undo [Z] (25 levels of redo [Y]) when editing a character.  Navigating will clear the undos/redos.   And there is a virtual clipboard which you can copy[C]/cut[X]/paste[V] a single character.   Note in this program you do not use the Ctrl key for clipboard as you do on a PC.

Notes:

• When launching the program for the first time, the ROM font will be copied to RAM, including moving the start of programs up to $1800 past the RAM characters.   Subsequent runs from that address will not recopy from ROM.  If you want to restart fresh from ROM, either reset your computer and run again, or POKE 44,16:SYS 6157.  You don't have to memorize the entry point, you can also LIST the line of BASIC that calls into the entry point.
• Saving overwrites FONT.BIN.  So if you want to save your work permanently, it is recommended to rename your file to something else.
  OPEN 15,8,15,"R0:COOL=FONT.BIN":CLOSE 15
• To LOAD your font for editing, be sure to run the program at least once, then load before running to enter back into edit mode.  Be sure to include the ,1 otherwise you will wipe the font editor out of memory, then best to restart your Commodore and try again.
  LOAD "COOL",8,1
• Pressing COMMODORE+SHIFT while in programmable characters will shift to a second set of characters which we don't have room for in RAM, so you will see bitmapped images of the program and video memory.   Press the key combination again to return to the first set of characters. [Disabled in the C64 port]

Update 2024 April 20: also ported to Commodore 64

Update 2024 April 26: more documentation

Description of key operations since added to Commodore 64 version

H - hide UI except pixels and character for a minimalist experience

/ - swap between two RAM character sets (C64 version edits total of 512 characters) 

F1 - foreground color

F2 - cursor color 

F3 - background color

F4 - character set 1 color

F5 - border color

F6 - character set 2 color

F7 - large pixel set color (editor)

F8 - large pixel cleared color (editor)

, - change titles color

. - change menus color

1,2,3,4,5,6,7,8,9,0 - select theme (colors and grid mode)

 As the C64 has a different memory layout, video memory is at a lower address $0400 and more memory available, the memory map is a bit different.  The start of the program is still at $1800, but the programmable characters are now from $0800 to $17FF, a full 4K (512 characters). 

Note that only the first character set (256 characters) is visible at this address without moving the character set to another location (planned for future).  But the editor can handle this by swapping the character sets in RAM for editing, swapping them back and forth, so one set is always edited from the lower $0800-$0FFF range that is visible.  Just be sure to swap back to the first set before saving, otherwise the character sets will be out of order.

To use both character sets in your own programs, it is necessary to manually relocate them or load them at another address, unless you use the swapping technique used by the editor.

It is not presently possible to use raster interrupts to show both sets because the second set is at an address that is mapped to ROM characters instead.  Another reason it is planned to move these in the future, for example to $3000-$3FFF but in the middle of BASIC RAM it may be too challenging to be useful to others.

Probably a better solution is to move both VIC-II memory to another bank of 16K, which also requires moving video memory.   Say bank 4 with characters at $F000-$FFFF, and video ram at $CC00-$CFFF.  Then move the start of BASIC to $0400, resulting in 39933 (39K) bytes available for BASIC, an increase of 1K the size of the video screen memory.

Leaving the editor, you have lost 4K of RAM from BASIC.  To reclaim 2K for the not visible second character set, POKE 44, 20: POKE 20*256, 0: NEW but don't load any of your double character sets or you will wipe out the first 2K of your BASIC program.   Best to leave 4K lost at start of BASIC in that case, or resize your character sets to a single set.

We're in the weeds here.   Back to the fun -- please enjoy the programmable character sets and the graphical opportunities they provide!

Update 2024 April 27: raster interrupts implemented as described above, with two sets on screen, and working area using ROM font so doesn't change.  Second set is copied to $3800-$3FFF for display purposes, while the two sets remain at $0800-$17FF.

Update 2024 April 28: themes implemented (10) and grid mode added, new C64 keys updated above.  Themes allow quickly changing between color sets and grid options using the numeric keys.

Update 2024 May 1: wrote an article on moving video and programmable character memory.

Update 2024 May 4: have fixed many issues, and more enhancements, including moving programmable characters to $2000-$2FFF to make more usable, eliminate need to have separate edit/view copies.  But loses more BASIC RAM ($0800-$1FFF 6K now available for other uses) while reserving memory for characters.

Primary Color Theme