The serial communication module uses the 16c550 I.C. to interface with a PC or other compatible device. I am using 9600bps,N,8,1 setup in my machine but you can select all other formats that this chips support. The conversion of signals (12V,-12V) to (5v,0) is done by the MAX233, this chip does not need any external capacitors like the max232 does.
JP9 should be jumpered if you want to use the Interrupt signal of the 16c550. Another way to use interrupts is through J9 connector, use a jumper cable to one of the extension pins (1-6) and then you can further process this signal before it reaches the Int signal of the Z80. This is how i ‘ll do it and i already designed a special module to handle all interrupts from all devices using IM1 of the CPU.
You should use jumper cables for the three connections on the upper layer, so you can make it as a single layer PCB.
Schematics
PCB
