VT180 with ImageDisk and Gotek Drives

VT180 Robin is a CP/M system from Digital (DEC), released in 1982. 

The VT180 system is basically a VT100 Terminal with VT18X Z80A CPU board and RX180 Dual Floppy Disk Drive unit. The Z80A CPU runs at 4.0 MHz [1]. 

The RX180 Floppy Disk Drive unit contains two Shugart 400L drives. The drive configuration is single-sided double-density180KB, which is compatible with the floppy disk drive for IBM PC 5150. ImageDisk tools can handle the disks and images for VT180.

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Several VT180 disk images are found on bitsavers.org. They are '*.P75' files, which are actually raw dump images. It looks like that they are the only VT180 disk images on the Internet.

This page describes the detailed information about how to use ImageDisk tools for VT180. Here are some additional tips:

• You can connect the Shugart drive inside RX180 directly to the FDD cable from your pc. 1) Use Drive B (the right hand side drive) of RX180, without altering the dip switch settings [2]. 2) Connect the drive to the "Drive A" connector of the FDD cable. The "Drive A" connector is located at the far end of the cable to the connector to motherboard.
  
  
• Use the following command to convert the *.P75 image files to *.IMD:
  
  bin2imd fname.p75 fname.imd /1 N=40 SS=512 DM=5 SM=1-9
  
  
• Use the following command to write/read the VT180 disks on the PC:
  
  imd /a c=40 ds=0 lr=250 s=1 il=1
  
  and then within the ImageDisk app, specify the remaining parameters as you format/read from/write to a disk:
• Sector size: 512 bytes/sector
• Tracks per sector: 9

The VT180 runs CP/M Version 2.2. The dual drive configuration seems essential to this system. Single drive system requires frequent disk swaps, which tend to cause the Ctrl-C and BDOS error situation.

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The Gotek Drive is a modern solution for floppy disk drives. It is basically a PC-compatible floppy disk drive emulator using USB flash drive. By installing a third-party firmware called FlashFloppy, it can emulate much wider range of drives.

Two Gotek drives can replace a whole RX180 unit. The following four steps are required.

1. Install the FlashFloppy firmware

Go to FlashFloppy Wiki page and follow the instructions. The stm32flash tool is required to write the FlashFloppy firmware into Gotek drives. On macOS, stm32flash can be installed using Homebrew:

brew install stm32flash

2. Configure ff.cfg and img.cfg

These are the ff.cfg and img.cfg files for VT180. These files can be placed in the root (or /FF) directory of the USB flash drives.

3. Prepare the disk images

This is the easiest part. Simply rename the *.P75 files to *.P75.DSK, to make them recognized by the FlashFloppy firmware. For example, you can rename the system disk image (on macOS terminal):

mv VT180CPM.P75 VT180CPM.P75.DSK

Place these disk image files in the root directory of the USB flash drives.

4. Connect Gotek drives to VT180

This is a tricky part. In order to connect two Gotek drives, a standard 34pin FDD cable is required.

First, connect the 37 pin VT180 Disk Interface port to the FDD cable: 

Next, connect two Gotek drives to the Drive A and Drive B connectors of the FDD cable. Note that a group of wires (pin10 through pin16) on the cable are 'twisted' for Drive A connector. As a result, the 'SEL0 L' signal from VT180 appears at pin 16 of the Drive A connector. Considering this situation, the jumper settings for the Gotek drives are as follows:

• Gotek Drive A: MTRON
• Gotek Drive B: DS1

Also connect the power pins (+5V and GND) of the Gotek drives to a proper power source.

Set the USB memory modules to the Gotek drives, turn on the power unit for them, then trun on the VT180. To the prompt from the system ROM, type 'A' to boot from the A drive. The CP/M system starts up:

What's next? Maybe I can write some programs on it, or make an enclosure for the dual USB drive unit.

Note:

1. Although Wikipedia explains that the CPU of VT180 CPU is a 2 MHz Z80 (based on Wikipedia page as of Mar. 2021), VT180 Technical Manual clearly states that VT180 is running a 4.0 MHz Z80A CPU.
2. With this configuration there is no terminator block on the floppy cable, but it seem working fine, probably because there is no daisy-chained cables in this small configuration.