Quadra 700 overclocked at 37.5 MHz

[Phipli]

I assume a standard mac 8 pin mini-din serial cable will have all lines connected at both ends, but whether Kermit or any other terminal program on the mac can be made to actually use RS422 I just don't know.

Yup, a standard apple serial cable works straight between machines.

Connected like this serial will just basically be RS422 I think - there isn't a 232 and a 422 mode. RS232 from a mac is more of an electrical bodge that involves clamping one side of the pair to gnd and being slightly out of spec. Macs don't work with some more recent RS232 devices that themselves are being a bit easy going with the specification. I have a serial box that won't work on my beige macs because of that.

 

[lobust]

Yup, a standard apple serial cable works straight between machines.

Connected like this serial will just basically be RS422 I think - there isn't a 232 and a 422 mode. RS232 from a mac is more of an electrical bodge that involves clamping one side of the pair to gnd and being slightly out of spec. Macs don't work with some more recent RS232 devices that themselves are being a bit easy going with the specification. I have a serial box that won't work on my beige macs because of that.

Good to know!

I'm kind of surprised, given that the macs serial ports are rs422 and most of Apple's serial peripherals are rs422, that Snooper's loopback test cables are wired for rs232 operation...

 

[Phipli]

Good to know!

I'm kind of surprised, given that the macs serial ports are rs422 and most of Apple's serial peripherals are rs422, that Snooper's loopback test cables are wired for rs232 operation...

Could you verify his pinout? I notice he says he "figured it out" and this "passes", not that he measured a cable.

Are... Pins 6 or 8 (TX+ and RX+) connected to anything else in your loopback? Is pin 4 (Gnd) connected to anything else?

 

[timtiger]

Are... Pins 6 or 8 (TX+ and RX+) connected to anything else in your loopback? Is pin 4 (Gnd) connected to anything else?

These are the connections on the loopback cable (tested various other combinations, this was the only one working):

RXD+ <> TXD+
RXD- <> TXD-
GND <> CTS+ (HSI+) <> RTS+ (HSO+)

 

[Phipli]

These are the connections on the loopback cable (tested various other combinations, this was the only one working):

RXD+ <> TXD+
RXD- <> TXD-
GND <> CTS+ (HSI+) <> RTS+ (HSO+)

I might be being daft, but that doesn't look like it is testing the handshaking? If they're tied to gnd?

 

[lobust]

These are the connections on the loopback cable (tested various other combinations, this was the only one working):

RXD+ <> TXD+
RXD- <> TXD-
GND <> CTS+ (HSI+) <> RTS+ (HSO+)

I might be being daft, but that doesn't look like it is testing the handshaking? If they're tied to gnd?

Yeah they should definitely not be grounded. Otherwise, OP's loopback cable is differential. Is this an original cable or one that you've made? Branchus' reverse engineered cable that he posted over on TD was single ended (RxD/TxD- only and handshake, also I admit that I did not read the rest of the thread, so this may be discussed).

Snooper serial loopback plug

Hi all, The Snooper software (originally made by Maxa, then later by Central Point Software) used to include a NuBus diagnostic card as well as a small, black, serial loopback plug for testing the serial ports. I'm not too fussed about the card, but does anyone have one of these loopback...

tinkerdifferent.com

 

[Phipli]

Yeah they should definitely not be grounded. Otherwise, OP's loopback cable is differential. Is this an original cable or one that you've made? Branchus' reverse engineered cable that he posted over on TD was single ended (RxD/TxD- only and handshake, also I admit that I did not read the rest of the thread, so this may be discussed).

Snooper serial loopback plug

Hi all, The Snooper software (originally made by Maxa, then later by Central Point Software) used to include a NuBus diagnostic card as well as a small, black, serial loopback plug for testing the serial ports. I'm not too fussed about the card, but does anyone have one of these loopback...

tinkerdifferent.com

That's what I was saying and why I suggested taking the measurements- his phrasing implied that it wasn't reverse engineered... he had an idea, tried it, and the tests passed.

 

[timtiger]

he had an idea, tried it, and the tests passed.

That’s it

On sunday I assemble a new one the way Branchus reverse engineered it. Sorry for my foolish acting!

 

[lobust]

That’s it

On sunday I assemble a new one the way Branchus reverse engineered it. Sorry for my foolish acting!

Ideally (IMO) you should use a combination of both - your current loopback cable has both TxD/RxD - and + connected which is technically correct, and then just HSKi to HSKo. Grounds should not be connected to anything for a short loopback cable.

As an aside, I am quite unimpressed with Apple's decision to make their serial port part differential and part single ended. That seems very hacky to me.

In case you missed it in my previous post, I think it would be more enlightening to learn what signalling scheme your other printers use. You said specifically that you tried an ImageWriter II which we know is differential, but I'd like to know about the others you tried. Whether the others are rs422 or rs232 would be useful data points. You already proved that rs232 (presumably with software flow control) works, at least well enough to echo some ascii.

 

[Phipli]

As an aside, I am quite unimpressed with Apple's decision to make their serial port part differential and part single ended. That seems very hacky to me.

It gave us built in really fast serial and networking, plus compatibility with common RS232 products. Local talk wouldn't hsve been a thing without it. I'm not complaining. I know what you mean, but it has always worked just fine with other compliant kit. The only thing I had trouble with was a late 90s lazy, probably 0 and +5v RS232 implementation.

On sunday I assemble a new one the way Branchus reverse engineered it. Sorry for my foolish acting!

Wait, what? But your pinout doesn't match the one I was looking at from his post? I'm really confused. Where did you find the information, do you have a link?

There is a chance that connection to ground on the flow control in the tester has damaged the flow control on your Q700. I don't recommend you use that tester on any other machines.

 

[timtiger]

your pinout doesn't match the one I was looking at from his post

Additional to Branchus‘ pinout I had RxD+ on TxD+ connected and GND to HSKi to HSKo. There are several pinouts for rs232 and rs422 out there in the www - very confusing. That was „my“ best-of version which was obviously no good idea.

I don't recommend you use that tester on any other machines.

You’re right, got that…

There is a chance that connection to ground on the flow control in the tester has damaged the flow control on your Q700.

I see Though I hope not; the failure appeared before the loopback/tester has come to use.

Ideally (IMO) you should use a combination of both - your current loopback cable has both TxD/RxD - and + connected which is technically correct, and then just HSKi to HSKo.

I’ll build a new loopback plug with GND connected to nothing, TxD- to RxD-, TxD+ to RxD+ and HSKi to HSKo. An extended version so to speak. Right @lobust @Phipli?

You said specifically that you tried an ImageWriter II

Yes.

I'd like to know about the others you tried

StyleWriter II: Apple-style RS-422 asynchronous serial (according to https://vintageapple.org/macmanuals/pdf/StyleWriter_II_1992.pdf)

LabelWriter II: Found nothing specifically. The docs for its predecessor (lookalike cable) are saying „Bidirectional, serial RS232 using transmit, receive and ground. Protocol is XON/XOFF o r CTS, I9.2K baud, 8 data bits, no parity.“ A pinout is also included in the docs on page 25 (https://cybarcode.com/sites/cy/files/manuals/costar/labelwriter_xl_user_manual.pdf and https://allpinouts.org/pinouts/cables/miscellaneous/costar-dymo-labelwriter-rs-232/) I can measure it with the multimeter on sunday.