OVERVIEW OF THE FACILITY
The Virtual 2315 Cartridge Facility implements a virtual version of the 2315 disk cartridge that would be inserted into the disk drive in the IBM 1130. It works in hybrid mode with the disk drive, thus a physical 2315 is placed in the drive and spun while the data is provided by the facility.
The drive spins the cartridge, the arms seek in and out as programs access the virtual cartridge - essentially everything the same except the heads don't fly down on the cartridge and the data is from the emulator. The timing as well as the physical sensations are just the same as if the heads were actually involved.
This leverages the RK-05 Emulator designed by George Wiley, but with substantially rewritten logic to emulate a 2310 disk drive and to work in the hybrid mode which is unique to the Virtual 2315 Cartridge Facility. A micro SD card is inserted in the emulator box, containing the virtual 2315 disk cartridge contents. It is loaded into the facility and then waits for the physical disk drive to spin up.
An interface board intercepts the signals between disk drive and the IBM 1130 controller logic. The cable which is normally plugged into the disk drive instead plugs into the interface board. A cable wired to the interface board is plugged into the disk drive instead. The board also accepts two ribbon cables from the RK-05 Emulator box. Finally, it is powered from the 1130's 12V DC supply.
In addition to the signals for the disk drive, we intercept two other switches on the disk drive. One of them indicates that the drive is unlocked to permit the introduction or removal of a 2315 cartridge. The other is the Run switch which is turned on to spin up the drive.
The operation of the facility is straightforward. A micro SD card sits in the emulator box. When the emulator box has its switch toggled to activate the image, the cartridge image is read in to the emulator. With a real 2315 cartridge inserted in the drive, the Run switch is turned on. The motor starts spinning the cartridge. After 90 seconds, as long as the emulator had a virtual cartridge loaded, the drive believes it has loaded the heads onto the disk and it turns on the File Ready lamp.
The user operates the 1130 and runs software exactly as they would if the facility was not installed. When the user turns off the Run switch on the disk drive, the emulator will write back any changes to the virtual cartridge image on the mico-SD card at the same time that the real cartridge is slowing to a halt. Finally, the Unlock lamp comes on the 1130 console.
INTERFACE BOARD INSTALLED INSIDE 1130 AND WIRED TO POWER AND SWITCHES
I tapped some holes in a support frame inside the 1130 and screwed the interface board into place. It also has wires from the DC 12V and ground, plus one wire each to the Disk Unlock switch on the drive and Unlock lamp on the machine console.
The cable from the 1130 controller logic is plugged into the back of the interface board. A cable from the board is plugged into the card cage on the disk drive. Two ribbon cables are plugged into the board to connect it to the RK-05 Emulator box which is mounted on top of the disk drive, accessible by lifting the top cover of the 1130. The emulator box is also wired to the +12V power of the 1130, so that it only comes on when the 1130 is powered up.
NEW VERSION OF PCB BEING FABRICATED
I improved the design in several ways. A mode switch was added, I did away with the sensing of the Run switch on the disk drive, and I added a circuit to light the Unlock lamp on the 1130 console when running in virtual mode.
The PCB will have a tiny slide switch which sets the Virtual 2315 Cartridge Facility to either virtual or real mode. In real mode, the disk drive inside the IBM 1130 is active, producing the sector and index pulses as well as physically seeking the arm in and out. In virtual mode, the disk drive is purely emulated and the physical disk drive is not used at all.
The Unlock lamp is a 48V bulb that is grounded by a microswitch in the disk drive whenever the solenoid is activated that allows the drive to be opened and a cartridge inserted. For the virtual mode, we will pull the line down to ground to cause it to light when the emulator box is ready to have a virtual 2315 image 'loaded' into the disk drive.
TESTED END TO END CONNECTION TO THE RK-05 EMULATOR BOX
I probed the connections in the RK-05 emulator card and the other end of the signal at either the disk drive backplane pins or the 1130 controller logic backplane pins, depending on the signal. This ensured that the cabling and the interface board design was correct.
I used the old PCB to verify the connectivity and will continue with it while waiting on the new board to be delivered - it has some bodge wiring and other changes to make it electrically identical to the new design.
ONE ISSUE WITH A CONNECTOR TO BE RESOLVED
I have an intermittent contact on pin B12 of the connector that plugs into the 2310 (internal disk) drive. It appears that the connector's opening is a bit wide and the pin on the disk drive's SLT board is perhaps a bit narrow. Wiggling the connector causes the connection to drop in and out. I will work on this before I move on to actual testing of my logic and code for the RK-05 Emulator box, now the Virtual 2315 Cartridge Facility box.
I circled the connector hole for B12. Visually it doesn't look any different but there is an issue with the connection for that pin to the hole.
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