DEC VT180 (aka “Robin”)

This webpage has some notes about a few aspects of the DEC VT180. It is mostly focussed on Kermit, and the processing of making bootable floppy disks from images that already exist online.

Note: To reset the VT180, press SETUP then 0.

Using Kermit on the VT180

The “VTKERMIT.P75” disk image on bitsavers is a bootable CP/M 2.2 disk with Kermit V3.0 and other programs on it.

The sign-on messages look like this:

CP/M VERSION 2.2 (1.1)
(C) 1981 Digital Research, Inc.

B>KERMIT
CUCCA/DEC VT18X Kermit-80 - ver 3.0

Kermit-80>

Unfortunately there is no manual on the disk itself, and I haven’t been able to find any documentation for this version of Kermit online. The online documentation for Kermit contains a large number of commands that aren’t present in this version. It does however have a HELP command, as follows:

Kermit-80> HELP
BYE to host and exit to CP/M
CONNECT to host on selected port
EXIT to CP/M
FINISH running Kermit on the host
HELP by giving this message
LOG the terminal session to a file
LOGOUT the host
RECEIVE file from host
SEND file to host
SET a parameter
SHOW the parameters
STATUS of Kermit
Kernit-80>

Kermit uses the “Communications” port, which is the DB25M that is built into the VT180 PCB. It gets its baud rate from the VT100’s SETUP “B” page. The other line parameters (data bits, stop bits, parity) can be changed using the CP/M PSETUP program, but by default they seem to be 8 data bits, 1 stop bit, no parity.

I downloaded the 32-bit version of Kermit for Windows (Version 0.85 dated 8 January 1998) and installed it on my X1 Carbon laptop. Using a USB-to-DE9 RS232 adapter, I was able to establish a 2-way text link between the VT180, and my laptop at 9600 baud (8 data bits, 1 stop bit, no parity).

I ran into some problems when trying to “SEND” a file from the laptop to the VT180. It would always fail, even though it was just a one-line text file. Once I reduced the speed to 300 baud, the transfer went through just fine. I did try with no handshaking and with XON/XOFF, but this made no difference. Note I was only able to change these settings at the laptop end – I couldn’t figure out the commands (if they exist) to make changes at the VT180 end. Selecting Hardware handshaking just resulted in no data flow (my cable had DTR/DSR handshaking wired, but not RTS/CTS).

– Don’t use lower case filenames
– GET command works. Need to specify th full path (eg C:\JUNK\MAL2.TXT)

RX180 Cabling

The VT180 connects to the RX180 external disk drive cabinet via a DB37M-to-DB25M cable, DEC P/N BC26K. The cable connects to J2 (DB37F) on the back of the VT180. The other end connects to the RX180 DB25F furthest from the power socket. It is important to connect the cable to this DB25F (not the one closest to the power socket) so that the terminating resistors on the first (left-hand) floppy drive are at the end of the cable train. The other DB25F socket is left unconnected (ie no terminator). This description applies to a system with only one RX180 (ie 2 drives in total).

A quick check of J2 with a multimeter shows that ALL odd numbered pins are connected to GND.

Henk’s website shows the pinout for the BC26K cable, if you need to make one. It shows that only 21 wires are used.

Inside the RX180, a 26-way ribbon cable is chained between the DB25F (near edge of back panel) to Drive 1 then to Drive 0 then to the other DB25F. One conductor (probably #26) is not connected to the DB25F connectors. Pins 1-5 and 31-34 of the floppy drives are NOT connected to the DB25F connectors. This isn’t a problem for the SA400, as Figure 9 of the SA400 OEM Manual shows that pin 1-6 and 31-34 are unused. Later model 5.25″ floppy drives used pin 34 for /READY (and later the pin was repurposed for /DISK-CHANGE) but the SA400 does not generate a /READY signal.

Here is an expanded version of Henk’s table, showing the connections inside the RX180 enclosure. I don’t have an original BC26K cable and so haven’t been able to verify against the actual cable. Instead I have relied on Tables 3-6 and 6-12, and the Disk Drive Controller Block Diagram at Figure 6-29, in the VT180 Series Technical Manual (DEC P/N EK-VT18X-TM-001).

Disk images on Bitsavers

Will Kranz contributed some VT180 disk images to Bitsavers -> Bitsavers VT180 disk images. Based on file dates, it appears they were contributed in 2007.

Will refers to these disk images on this webpage, where he says:

When I published the Technical Reference scans I included copies of my system software disks which are available at BitSavers. Caution, these are raw physical disk images obtained on a faster machine which was capable of track at once reads of the media. To recover the data you must deal with the sector interleave the VT-180 disk controller imposed. The VT180DSK.LST is a list of the disks by DEC part # with a very brief description. If memory serves they were all bootable, the two key disks VT18DIAG, the diagnostics disk, and VT180CPM, the CPM 2.2 boot disk, definately were bootable. I believe everything in this list with a ‘BJ-” part number came in the original distribution. SELECT was the distributed editor, SUPERSPL was the associated spell checker, and SINSTTCH was a tutorial for Select. For programming I had the distributed MBASIC, Microsoft’s Mbasic, and TPASCAL a version of Turbo Pascal I purchased separately. MULTIPLN is the distributed spread sheet program. VTKERMIT contains a compatible version of Kermit from Columbia University and another serial communications program, POLYGON.

The file VT180DSK.LST explains that these images have been written as direct dumps of sector data in the order they physically appear on the disk, using a program called “wdcopy”. No sector header information is included in the images.

The VT180 disk format is 40 track, single sided, 9 sectors/trk, 512 bytes/sector, 250 kbps MFM. This gives a disk capacity of 180KB.

These images can be converted back to IMD format with ImageDisk’s BIN2IMD utility. For example:

BIN2IMD VT180CPM.P75 VT180CPM.IMD N=40 DM=5 SS=512 SM=1-9 /V1 /1 C=BJ-M074B-BV~VT180~CP/M~2.2

The “C=” parameter is just a comment that gets stored in the IMD file. It is a useful way to store information from the disk label. The tildes shown above are converted to space characters by BIN2IMD. Normally I also include a /C switch in the above command, but it caused errors in a couple of the lines, seemingly due to long line length.

Once the images are in IMD format, ImageDisk can be used to write the IMD image out to a real 5.25″ 40-track disk.

The VT180CPM.P75 disk (after being written out using ImageDisk) gives the following greeting when booted:

CP/M VERSION 2.2 (1.1)
(C) 1981 Digital Research, Inc.
A>

and issuing the DIR command yields the following:

A>DIR
A: LOAD     COM : XSUB     COM : ASM      COM : DDCOPY   COM
A: DDFMT    COM : DDT      COM : DUMP     COM : ED       COM
A: PIP      COM : STAT     COM : SUBMIT   COM : SYSGEN   COM
A: PSETUP   COM
A>

Links

ZIP file containing the VT180 disk images referred to above (converted to ImageDisk format) is available for download here. This ZIP file also include a .BAT file with the BIN2IMD commands.

Henk Gooijen has a really nice webpage about his VT180 including how to make your own RX180 cable.

There is some information and pictures on Eric Klein’s website.

There is a some information about RX180 drives and cables on this thread on VCFED’s forums.