After last weekend's creation of the uTerm terminal adapter, it was time for setting up the Z80-MBC2, the main CPU PCB.
Creating the Z80-MBC2
As usual, the kit from McJohn was complete, well sorted and of high quality. After sorting the components I started with the usual sequence, i.e. resistors and diodes first, followed by LED, transistors and conductors. At the end I have soldered in all sockets and connectors.
The connection between MBC2 and uTerm is realized with 8-pin pin headers - male on the MBC2, female on the uTerm. Two mounting variants are possible:
- Both PCB "laying horizontally": we need the angled pin header for the MBC2, or
- MBC2 and uTerm are mounted with a 90° angle, i.e. uTerm is "standing": here we need a straight pin header.
I have chosen variant 2 and therefore soldered the straight pin header. To securely connect both PCB, matching 3D-printed plastic angles are part of the kit, together with plastic screws and stand-offs.
Testing the MBC2- and uTerm-PCBs
A first test of the PCBs was done without inserting the chips. The MBC2 and uTerm were connected, incl. the short 2-pin power supply cable (5V). After connection of the main power supply, I tested correct levels of GND and +5V on all sockets and connectors.
After all looked pretty OK, I inserted the chips into their corresponding sockets, connected the keyboard and the Monitor and powered everything up again. Et voila: the board started immediately, showing the boot messages on the screen! Unfortunately, the PS/2-Keyboard seemed not to work at all - no reaction on pressing the keys.
Serial Connection
Before checking the reason of the non-functional keyboard, I wanted to finish testing of the MBC2 itself. So, I decided to setup a serial connection to my PC. Part of the kit was a USB-to-serial cable. Unfortunately the pinout of this cable was not documented, so I had to do some web research. The following pinout seems reasonable:
- black: GND
- red: +5V
- white: RX
- green: TX
But no connection to my MAC was possible, using the cable. The device was simply not recognized. Luckily I have a FTDI-adaptor at hand (a small PCB from AZDelivery). To use this adaptor I had to create a cable, connecting the FTDI with the pins of the serial interface on the uTerm. The pinout of this cable had to be as follows:
| Pin FTDI | Signal | Colour | Pin MCB2 |
|---|---|---|---|
| 1 | DTR | brown | 1 |
| 2 | RX | white | 2 |
| 3 | TX | green | 3 |
| 4 | +5V | red | 4 |
| 5 | CTS | NC | NC |
| 6 | GND | black | 5 |
The FTDI board was recognized by my MAC immediately! With the following command inside the MAC-Terminal you can find out the Device ID of the FTDI:
ls /dev/cu.usbserial-*
And the next comand starts the terminal session with the uTerm & MBC2:
screen /dev/xx.usbserial-XXXXXXXX 115200 –L
Of course, you have to replace "XXXXXXXX" with the device ID retrieved by the "ls" command.
The parameter "-L" will allow logging of the whole terminal session. The session can be ended, using Ctrl+A and then Ctrl+K.
Setup of MBC2 and uTerm
Using the terminal session, I was able to sent key-strokes and complete the initial setup of the system, e.g. setting correct time & date for the RTC. A closer examination of the uTerm, to find out the reason for the non-working keyboard, led to no result. All components were of correct value at the correct position, no bad solder joints or shortcuts could be identified. Finally I tried it with a different PS/2-keyboard - and then it worked. Maybe my "more modern" PS/2-keyboard I tried initially, has some incompatibilities, who knows. Anyway, the vintage keyboard works as a charm!
