POST CODES AND ACTIVITY AS AN INDICATOR OF OPERATION
The SBC6120 has a set of LEDs that show the progress of startup and any problem that is encountered. The goal is to have the four LEDs end with ON-off-off-ON which occurs with the SBC6120 by itself. If the IOB6120 is added but the FPGA is left active, an illogical state since the firmware for the component was not yet loaded, gives us an error status of ON-ON-off-off which is a memory error. The IOB6120 takes part of the memory range for its function but is not responding properly to the SBC6120 given the lack of firmware. This makes sense.
JUMPER TO DISABLE FPGA ON IOB6120 PRIOR TO LOADING FLASH
Adding a jumper to a pair of pins disables the FPGA and now the system starts up to the normal ON-off-off-ON state, indicating the tests are complete and the monitor is running. The next step would be to connect with a serial port and terminal program, to communicate with the monitor on the board. This is a positive sign in the early checkout of the IOB6120 board.
POWER CABLE INSTALLED TO FLASH CARD EMULATED IDE DISK
The SBC6120 provides an IDE disk interface, to which I have connected a board that uses a CF card to emulate a disk drive. The board needs power from the main SBC6120 board, provided using a PC four pin to mini four pin cable as typically connected to disk, floppy and CDROM drives.
SIGNS OF LIFE PRIOR TO TERMINAL CONNECTION
With the board powered, I see it flash when I boot the PDP-8, the front panel lights loop for a bit and I take this as an indication that the OS/8 image has been started properly. Again, until I connect with a terminal program this are suggestive but not definitive indications of health.
FIRST GOTCHA FROM ILL CONSIDERED ACCEPTANCE OF MS WINDOWS 11 UPGRADE
Having been cajoled, hounded, beseeched, urged, prompted and pestered by Microsoft to upgrade my Windows 10 system to Windows 11, along with a projection that everything will work fine after an upgrade, I finally in a moment of weakness acceded to the upgrade. In my heart I knew I would pay the price, but all the programs I tried such KiCAD worked properly which lulled me into false confidence.
Alas, when I plugged in my USB to serial adapter, the device manager entry listed the driver as "upgrade to windows 11 version". I downloaded the latest Prolific driver, only to have the driver message change to "HA hardware not supported". Time to buy a replacement that is supported in Windows 11.
MOVE TO WINDOWS 8 BASED SURFACE PRO TO ATTEMPT TERMINAL CONNECTION
In the interim, I grabbed my Surface Pro, running Windows 8, to attempt the terminal connection. I wired up the connection between the USB adapter and the DB9 connector from the SBC6120, then powered up.
The screen output was bursts of gibberish, repeatable but not intelligible. I was not able to see valid output from the monitor.
MAY HAVE TOASTED THE USB TO SERIAL BOARD DUE TO REAL RS232 VOLTAGES
It was then that I realized that the SBC6120 produces real RS232 - meaning voltages in the range of + and -12V - unlike the 0 and 5V used with TTL serial connections. Both make use of a DB9 with the same signal names, but I may have very well have fried the adapter by presenting it with excessive voltages as well as negative excess swings.
I have a new adapter on order, Windows 11 capable, plus some RS232 to TTL adapter hardware. Hopefully when I have this on hand I can connect to and communicate with the SBC6120. That is essential in order to download the flash data to the IOB6120.
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