I am trying to bring a Cromemco 2-ZD system back to life. I have already safely brought up the power supply and everything checks out fine there. Reset circuit, clock signal all check out fine. Right now I just have installed the Cromemco ZPU, dynamic RAM, and 4FDC. The 4FDC houses the 2708 EPROM which has RDOS 1.1 on it. According to the manual, I should be able talk to it using a Terminal @ (up to) 9600 baud. The manual says I hit enter several times to calibrate the baud rate, and I should get an RDOS message back. I have tried all that, but I get nothing.
First of all, does anyone have a schematic for the 4FDC? I can't find one anywhere. This board uses the TMS5501 I/O controller which I am unfamiliar with.
On the 4FDC, I've hooked up my scope and traced the incoming serial signal from my terminal on PIN 2 of the DB25 connector. This goes to a 74LS241 - pin 17 / 2A4:
The only signal I see come out the other side looks like this - on pin 2 / 1A1:
FYI - this is a brand new 74LS241 chip. I'm a bit confused on what happens from here. I don't see the serial signal end up anywhere at the 5501.
Anyone have some recommendations on how to get this thing talking?
First of all, does anyone have a schematic for the 4FDC? I can't find one anywhere. This board uses the TMS5501 I/O controller which I am unfamiliar with.
On the 4FDC, I've hooked up my scope and traced the incoming serial signal from my terminal on PIN 2 of the DB25 connector. This goes to a 74LS241 - pin 17 / 2A4:
The only signal I see come out the other side looks like this - on pin 2 / 1A1:
FYI - this is a brand new 74LS241 chip. I'm a bit confused on what happens from here. I don't see the serial signal end up anywhere at the 5501.
Anyone have some recommendations on how to get this thing talking?