MIDI and Lynx

sage · January 7, 2018

Hi there,

Maybe a few of you wondered why there is (in the original BLL kit) a com program to interface the lynx with 31250baud to an Atari ST?

Short answere: The Lynx has some very weird baud rate setttings. The onyl useable for a normal PC is 9600baud, but 31250 matches exactly the MIDI specifications. And the Atari ST comes with a MIDI port.

Makes debuggin and uploading much much faster.

BUT (now comes the bad things):

MIDI is using a current loop (5V) while comlynx is level sensitive to 5V. Thus you risk either to damage something or you need some adapter. Nothign special, a simple optocoupler and a few resistors & diodes. Actually, the MIDI specs require that you decouple the MIDI In. PS: Did I mention that, if you "just" connect it by some passive resistors, the polarity of the signal is inverted?
And, you need to set the serial setting to 31250E1, because the lynx expects ALWAYS a parity bit. Very bad, because the MIDI specs are 31250N1. This can be done easily if you have a ST or PC where you can set the port parameters. You just have to remember to do it.

Q: Now, if I build me some adapter, could we use MIDI In to connect a Keyboard to comlynx?

A: No. (Reason 2). The Keyboard will send out data withou parity bit. The Lynx will reject the data bytes (even if you disable parity checking!).

A: Yes. If you but some "intelligence" inbetween. A simple microcontroller will do. Or a Laptop.

So, You connect the keyboard with a midi adapter to your laptop and use an configurable(!) second adapter to send it out including parity. Or, to make it a bit simpler, you send out the data by a normal serial port with 9600E1 setting, which interfaces directly with a standard serial-comlynx interface.

9600 is a bit slow for MIDI, thus the timing is a bit ... inaccurate. But: Its working!

Edited January 7, 2018 by sage