notes for pic18Test project, dvb 08

This is a little scratchpad project for understanding parts of the Pic 18F4550 and PICDME FS USB demo board.

Things I've Learned

MCC18 adds keyword "overlay" for semi-static variables
also rom char * for pointers into data memory


The examples put reset and irq vectors up at 0x800. But the chip really has them at 0. IF you have the boot loader installed, then that bit of code forwards the irq. But since I don't, I need to include vectors at 0x8 and 0x18.

The boot loader fits in 2k, and is a very stripped-down usb implementation.

At 12 mips, the clock divided by 46875 is 1/256th of a second. So, incrementing a word at that rate gives you both a reasonable high(ish) res timer (256ths, about 4ms) and a spot-on seconds ticker, in adjacent bytes.

PICDEM FS USB board port usages...

RA0 -- on-board potentiometer
RA1, RA2 -- hooked up to monitor power, usb in? something...
ra1 can be used, but pulling low triggers usb sleep...
RA2 -- drives max rs232, or cut trace JP6 to use
RA3 -- driven from max rs232, or cut trace JP4 to use
RA4 -- open
RA5 -- open (AN4)
(ra6, mentioned in datasheet, no pin)

RB0, RB1, RB2 -- spi to thermometer?

RB3 -- open
RB4, RB5 -- buttons on board
RB6, RB7 -- ISCP, open when programming cable removed


RC0 -- USB Sleep
RC1 -- open
RC2 -- open
RC3 -- not exist
RC4, RC5 -- USB
RC6 -- drives max rs232, cut trace jp5 to use
RC7 -- driven from rs232, cut trace jp3 to use

RD0, RD1, RD2, RD3 -- LEDs on board
RD4, RD5, RD6, RD7 -- open

RE0, RE1, RE2 -- open


Pins available on connector:
RA1
RB3
RB6 -- after cable removed
RB7 -- after cable removed
RC1
RC2
RC6
RC7