01-21-2006, 08:51 AM
To my knowledge the "progamming" port is 12V, same as the PC. Then there are 2 pins for TxD, RxD on the I/O lines that do +5V serial. I need three serial devices hooked up to this second channel. Can I use a 74139 chip 1 of 4 multiplexer and 3 74245 octal bus transcievers to make a serial bus? I would connect A and B on the 139 chip to two I/O pins on the stamp. Then Y0,Y1,Y2 would "strobe" the 245's at the CS pin 19 when the stamp is ready to talk to them. Could I simply connect the respective serial device to each of the 245 and only use two of the pins on the input side and connect the RX and TX from the output side of the octal bus drive directly to the STAMP serial port. I am confused because it looks like 8 bits are needed, but I only would need to connect two wires to each IC for input. I would simply connect each of the 245 outputs to a TX bus and a RX bus and connect those busses directly to the Stamp pins. I know I can build a 2 device switch using only one I/O line for select and using 74hc00,74hc02, but I need three. The devices are a socketmodem(look on halted.com - it's $4.95 each, not $56 like the CH1786A), video card from microlabs, and a ps/2 to serial mouse adapter from multilabs. On the other side, can anybody tell me if they think I would spend all the processing time switching between these devices and waiting for them to respond. I am actually trying to create a 2 player "TV" game using a modem. I want to just use a CB220(cube loc 220) it says it is pin compatible with the BS2 but includes AD conversion on chip and an attenuator. The same problem exists and the BASIC is different. There is no SEROUT on the CB220, so the instructions for using the ezVid 2.0 card from multilabs would be complicated. It does have a OpenCom statement for 0 being the 12V programmer port and 1 for the 5V serial on two I/O lines. the 220 is $34 dollars and they offer the programming board with a rs232 port for $5. It also executes at 36k instructions/sec at 18.xMhz. Can any body help clear up how I would create a serial bus to act like a N way multiplexer? thanks for any info.