Neutrik A2 serial port upgrade

[AudioplatinumService]

Hi to all..   

I am in process of upgrade one of mine audio measurement devices. This is an Neutrik A2, measurement sistem based on Z80 processor. Unit have one parallel port for printer and one option serial port for software control.

I want add serial port based on Z80 SIO and I have original documentation, but I want have after Z80 SIO one serial to USB adapter and with that I can use this machine with software control. Serial port is option card and today is not easy to find one. Original serial card is build with z80 SIO, max232 and some logic for level translating. When I add serial communication, then I can use original Neutrik software for taking screenshots from measurement and control whole unit remote.

In this post I attach original schematic with SIO and MAX232, and also my drawing with FTDI USB serial, my problem is how to solve clock for serial, in original board, clock is made with EXO3 - 19kHz programable oscillator, speed for using original software is 19200 and 38400. Can someone suggest some simple solution?

Cheers,
Damir

[Kean]

Yes, this should work - but a few observations

a) The EXO3-19 is a 19.6608MHz oscillator (not kHz).  The SIO requires a clock of 16x the baud rate.

b) Instead of the EXO3, just set up a fixed oscillator for the highest baud rate possible.  At x16, 38400 would be 614.4 kHz which could be generated by a common 3.6864MHz oscillator and a 6x divider, or 4.9152MHZ and a 8x divider.  With the Z80 SIO you may even be able to run at a higher baud rate if the software allows it, and eliminate the divider.  Something like the ECS-2100AX oscillator available on DigiKey for a few bucks.  There have been 614.4kHz oscillators, but they will be likely be pretty hard to source.

Check http://6502.org/users/dieter/uart/uart_3.htm for an example.

c) You will very likely want isolation between the device and computer.  You can see the opto-isolators in the original schematic.  A simple solution is to use an FTDI style adapter with the isolation already included.  I use the ones from seller Duppa on Tindie and they are really useful.  They have version with 4 or 6 pin connectors, depending on whether your need hardware flow control.  You could also do this with discrete opto-isolators, but may need to invert logic levels as per the original schematic.

https://www.tindie.com/products/saimon/debug-board-usb-to-rs232-isolated-serial-converter/
https://www.tindie.com/products/saimon/debug-board-usb-to-uart-isolated-with-flow-control/
Edit: Oops, the one with Arduino compatible pinout is this
https://www.tindie.com/products/saimon/isolated-usb-uart-converter-for-arduino-pro-mini/
And as you appear to be in the EU, you probably can't buy from Tindie - so try their website
https://www.duppa.net/shop/usb-to-ttl-uart-rs232-isolated-for-arduino-pro-mini/
FYI - I am just a happy customer of this product, and have no affiliation

[AudioplatinumService]

Hi Kean,

Thank you so much on your observation about my small upgrade, yeah.. I somehow miss freq. of oscillator, and now is all clear. I will prepare protoboard and make this with SIO and ECS-2100AX. I newer use Z80 SIO, but I saw that this is trivial circuit, just level conversion, clock and isolation, and this must work with USB serial converter. Original software work from 9600 till 38400bps. Now it is time for ordering some oscillator.. Z80 SIO is ready.

Regards,
Damir

Yes, this should work - but a few observations

a) The EXO3-19 is a 19.6608MHz oscillator (not kHz).  The SIO requires a clock of 16x the baud rate.

b) Instead of the EXO3, just set up a fixed oscillator for the highest baud rate possible.  At x16, 38400 would be 614.4 kHz which could be generated by a common 3.6864MHz oscillator and a 6x divider, or 4.9152MHZ and a 8x divider.  With the Z80 SIO you may even be able to run at a higher baud rate if the software allows it, and eliminate the divider.  Something like the ECS-2100AX oscillator available on DigiKey for a few bucks.  There have been 614.4kHz oscillators, but they will be likely be pretty hard to source.

Check http://6502.org/users/dieter/uart/uart_3.htm for an example.

c) You will very likely want isolation between the device and computer.  You can see the opto-isolators in the original schematic.  A simple solution is to use an FTDI style adapter with the isolation already included.  I use the ones from seller Duppa on Tindie and they are really useful.  They have version with 4 or 6 pin connectors, depending on whether your need hardware flow control.  You could also do this with discrete opto-isolators, but may need to invert logic levels as per the original schematic.

https://www.tindie.com/products/saimon/debug-board-usb-to-rs232-isolated-serial-converter/
https://www.tindie.com/products/saimon/debug-board-usb-to-uart-isolated-with-flow-control/
Edit: Oops, the one with Arduino compatible pinout is this
https://www.tindie.com/products/saimon/isolated-usb-uart-converter-for-arduino-pro-mini/
And as you appear to be in the EU, you probably can't buy from Tindie - so try their website
https://www.duppa.net/shop/usb-to-ttl-uart-rs232-isolated-for-arduino-pro-mini/
FYI - I am just a happy customer of this product, and have no affiliation