This code was developed by Ken Webster for his Time Source Monitoring Test System

14-bit core PIC source:

• http://ndsl226.dnvr.uswest.net/cgi-bin/tl.exe/Timemon/sermux/sermux_m.asm (cached 20000106) Master: This is code for the PIC16C74 which is connected to the SRAM 'as well as all the other (slave) processors. It is responsible for reading and writing from/to the other processors, buffering data in the, SRAM, and packaging and unpackaging data to/from routing packets.
• http://ndsl226.dnvr.uswest.net/cgi-bin/tl.exe/Timemon/sermux/sermux_s.asm (cached 20000106)Slave: This is code for the PIC16C73s which act as smart buffered UARTs for the main PIC16C74 processor.

PC Windows NT or 95 or 98 source to talk to PIC:

• http://ndsl226.dnvr.uswest.net/cgi-bin/tl.exe/Timemon/monitor/MultiplexerInterface.cpp (cached 20000106)

Uses CRC and checksum and packet serial number to detect corrupt or missing packets. Chop out code that supports channels if you only need one device connected (this app is for connecting multiple devices via a multiplexer). If need help feel free to email me at ken@webster.org

; Apply W to command-interpreter receive checksums
update_crx_checksums	xor	rCmdxs, W	;update plain checksum
	xor	rCmdcl, W	;update cyclic checksum
	add	rCmdch, W
	clrb	C
	rr	rCmdch
	snb	rCmdcl.0
	setb	rCmdch.7
	rr	rCmdcl
	mov	W, #$31
	add	rCmdcl, W
	snb	C
	inc	rCmdch
	mov	W, #$03
	add	rCmdch, W

void Checksum::Add(unsigned char c){    plain_checksum ^= c;
    cyclic_checksum ^= c;    cyclic_checksum += (unsigned short)c << 8;
    bool carry = (cyclic_checksum & 1) ? true : false;    cyclic_checksum >>= 1;
    cyclic_checksum |= carry ? 0x8000 : 0;    cyclic_checksum += 817;}