Well, I built a 20 mil (really TTL) to RS-232 adapter for my AIM.

I used a MAX232, and connected it according to the app note, which recommends using 1uf caps in the voltage doubler circuit.

I connected pin U on the 44 pin edge connector (TTY out) to pin 11 on the MAX232, and pin 14 to Rxd on the RS232.

I connected pin y on the 44 pin edge connector (TTY in) to pin 9 on the MAX 232 and pin 8 on the MAX 232 to RS232 Txd.

I connected the unused inputs (pin 10 and 13) on the MAX 232 to ground so as to not have floating inputs.

Did a continuity check with all connections and a voltage check, all seemed well.

I then connected it up to a terminal emulator at 2400 baud and inited the locations on the AIM for 2400 baud.

I've tried 1200 baud, and 2400 baud, 8 bits 1, 1.5 and 2 stop bits, odd, even and no parity, 7 bits, 1, 15, and 2 stop bits, odd, even an no parity.

When I transfer control from the AIM to the TTY in/out, nothing happens, no in, no out. I then press the space bar on the AIM and it starts sending characters, but all I see is y0' on the terminal display. When i put the KB/TTY switch on the AIM back to KB, the characters stop.

Any clues, where should I look next?

Any help or suggestions much appreciated,

AndyD

These are kind of general RS-232 debugging tips, but some terminal programs expect the hardware handshaking signals CTS, DCD, DTR, etc. Try disabling handshaking, as it isn't necessary for two pieces of equipment sitting a few feet apart on the same desk. Otherwise, you can write a short test routine in assembly or Forth or whatever. Just something to see if bytes are being sent and recieved correctly. It often helps to deal with the serial port hardware (UART) directly.

Resetting the UART and emptying the reciever buffer can also help. If the RS-232 cable gets unplugged and reconnected and you get a glitch on RX, this can get interpreted as a start bit by the UART and could also result in a framing error. With your own software you can just ignore things like this.

Cables can cause difficulties sometimes. Null modem cables will have RX to TX, TX to RX, and GND to GND, but they vary in how the handshaking signals are connected. I build my own null modem cables, with only RX to TX, TX to RX, and GND to GND. About the only RS-232 cables I trust are what might be called RS-232 extension cords. A male connector at one end, a female connector at the other, and pin 1 connected to pin 1, pin 2 connected to pin 2, pin 3 connected to pin 3, etc.

This was a case of several errors on my part that stacked up. I managed to get some useful info from a fellow AIM user from the Classic Computer list.

Escentially I had two problems:

1. When I used the MAX232 I didn't notice that thew signal was inverted at the output....Fixed by adding an inverter between the AIM and the MAX232. Worked just fine for output, since I inverted the TTL output from the AIM to the MAX232, then the output characters were transmitted and recongnized just fine.

2. When I added a TTL inverter between the MAX232 and the AIM, I ignored the fact that the AIM is expecting RS-232 input levels and TTL levels just weren't cutting it. I bypassed the MAX232 and the extra TTL inverter and just took the RS-232 straight to the AIM and eureka, it worked! Serial communication both ways, AIM to Mac, Mac to AIM.

This is not just a connection directly to the Mac, I had to use a USB to RS-232 converter from the Mac, then convert the RS-232 to levels tha AIM could use, but all is well.

BTW: I found a nifty terminal emulator program for the Mac to use as my terminal. It is ZTerm. Seems pretty good.

Well, thanks again for all the help,

AndyD

please remove this post

16 years… Is that a new record for a necro post?

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