A friend was given a 3174 controller, model 51R, which he in turn gave to me recently. This is a
controller with nine coax ports that can control up to nine 3270 series terminals. It is the base configuration, absolutely no options added. All the card slots in the cabinet are empty, since all the functions of the base configuration are implemented on the large motherboard (planar in IBM speak).
Therefore it has 1MB of storage, quite small if I really had many terminal attached. eBay sellers do offer memory modules which I could buy to boost the capacity but this doesn't seem warranted at the time. I has a single communications adapter that provides a V.35 link, 56Kb speed, which can operate in either BSC (IBM bisync serial) or SDLC (IBM SNA synchronous data link control).
It does not have cards to implement other connectivity such as Token Ring or ethernet. Nor does it have the Async Emulation Adapter card that will hook to ASCII terminals. Fairly bare bones but adequate for my purposes. Many of those cards are available, albeit at somewhat inflated prices, if I need them.
The base configuration comes with a single 5.25" floppy disk drive. While the larger models of the 3174 made use of high density 2.4MB drives, compounding the challenges for hobbyists, the low end models 51R and 53R used the same 1.2MB drives that were used in early PCs. Options existed to add a second floppy drive and/or a hard disk.
ARRANGING FOR DISKETTE FILES
As is so often true when finding these controllers today, they did not have the diskettes that are essential for proper operation of the controller. A Control diskette holds the code that is loaded when the controller is started up - a process called Initial Microcode Load or IML. A Utility diskettes has tools including those needed to build the customized configuration file that describes the terminals and the controller, such as the models and options installed.
I am very fortunate to have a friend who is a hobbyist working with these controllers who had the contents of the Control and Utility diskettes available in digital form. I have in hand the contents which could either be written to a real floppy diskette or put into a modern floppy disk emulator. I chose the latter route as it is easier and faster for me to pursue.
CONVERTING FLOPPY DRIVE EMULATOR
I bought a Gotek floppy disk emulator box which arrived today. This box hooks up to the floppy data and power cables, sporting a USB port where a memory stick is inserted. The memory stick holds many diskette images, which can be selected by pushbuttons on the front of the emulator box.
While it has firmware on it that is adequate for many floppy attachments, a much more powerful open source firmware exists called FlashFloppy that fully supports the 3174. The process of flashing the new firmware is multistep but not that difficult.
Attaching the emulator to the 3174 requires a small amount of hardware hackery. The 5.25" floppy drives have a PCB card edge onto which a connector attaches, but the Gotek comes with the standard 34 pin ribbon cable based IDC connectors that are used with 3.5" floppy drives. I have an adapter coming but I won't have it until Monday evening.
There are also some signal wires to check and a diode to add that tells the controller that the Gotek is ready. Nothing very challenging but tasks that need to be accomplished before I could IML the controller from the diskette images.
BRINGING UP THE 3174 - PRIOR TO EMULATOR ATTACHMENT
About all I could verify without real diskettes or the completed floppy drive emulator is to power up the unit to check that it passes the very primitive tests and then indicates missing/empty floppy drive errors.
It came up with all power supply voltages present and proceeded through its attempt to IML. I saw the display cycle back and forth between 57 and 58 a few times, then move rapidly through some numbers in the range of 1xx up to 113. The red access light on the floppy drive illuminated and blinked as it tried to read a diskette. It advanced to 114 for a bit and then to 130 where it remained. After two seconds at 130 it also illuminated the red Condition Check light on the faceplate.
The first two codes, 57 and 58, show the processor doing memory diagnostics on the 1MB of storage configured in the machine. The sequence starting at 1xx is the IML process itself. It is accessing floppy drive 0 during 113, but of course there is no diskette installed so that fails. It then moves to 114 which tries to access floppy drive 1. Eventually that will be my emulator but today it was not operational.
Status code 130 is the expected terminal state in this case. It tells us that an IML was not possible because the Control image was not found in the fixed disk drive nor in the two floppy drives. This hints that I have a working 3174 simply waiting for the microcode that I will install in the Gotek and hook up as drive 1.
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