RS-485 Adapters were originally designed using PIC18F2455 (24k flash) and PIC18F2550 (32k flash) in mind, but with the recent introduction of the PIC18F24K50 (16k flash) and PIC18F25K50 (32k flash) some serious cost savings will be achieved.
These new CPUs are pin compatible with the existing chips, almost $2 (US) cheaper, and have internal oscillators factory tuned to be accurate enough for USB full speed operation. This eliminates the need for an external crystal circuit including two associated capacitors bringing more than $1 (US) cost savings.
The Microchip Libraries of Applications v2012-08-22 (USB stack), MPLAB IDE v8.87, and MPLAB C compiler for PIC18 MCUs v3.43 support these new chips. I was able to successfully port my existing code using the new stack, and compile and program the chips using MPLAB.
Thanks to Dangerous Prototypes for bringing the news of these new MCUs to my attention. And to Microchip for providing samples so quickly. Some stock of these 5V SPDIP chips is currently available directly from Microchip and more supply will be available in the coming months.
Saturday, September 29, 2012
Friday, September 21, 2012
original design now implemented in Eagle and also did a two layer PCB layout. I used Seeed's PCB service to produce the PCBs, ordered parts from Digi-Key and assembled them by hand. There were two mistakes with the board. Somehow I didn't connect VCC from USB, and inadvertently connected VCC to VUSB. Three cuts and three jumpers later and the boards work fine.