HP 7970


Videos featuring my HP 7970E tape drive

My HP 7970E magnetic tape drive shows up in several videos, including my 9-track tape demo video, my ASCII art video, and my HP 7970 repair video.

HP 7970 A/B/C/E Overview

The HP7970 A/B/C/E are a series of 9-track, 1/2" wide magnetic tape digital reel drives. The 7970A, first released in 1970, has a density of 800 Characters Per Inch (CPI) and a tape speed of 37.5 inch-per-second (IPS). In 1971, the 7970B upped the speed to 45 IPS. The 7970C revision is an updated version the B with the same specs - as far as I can tell. The 7970E introduced in 1971 uses phase encoding, doubling the density to 1600 CPI. There are some rare 7970E units that can run at both at 800 and 1600 CPI, and some even rarer models that have the dual 7 track and 9 track heads, so they can read some of the very early IBM 7-track tapes. Finally, some 7970E are equipped with the optional HP-IB interface.

These tape drive units were originally meant to connect to the HP 2116, HP 2100 and HP 1000 M/E/F computer systems, but were also used in the HP 3000 computers. There are two types of units, Master and Slave. One master unit can be wired in a chain to 3 other slave units. The computer connects to the master unit. The slave units were cheaper, because they had less electronics in them. Instead they relied on the boards residing in the master.

The tape drives use a wide parallel interface, similar to Pertec. The interconnect cable hooks to three board edge connectors inside, namely to the write, read and control boards. On the computer side, two large edge connectors attach to a pair of interface cards. The interface cards are the HP 13181 for the 800 CPI HP 7970A/B and the 13183 for the 1600 CPI HP 7970E. The cable part number is 13181-60030.

The 7970E can be equipped with an optional HP-IB interface. It consists of an added HP-IB card is installed inside the unit, which connects internally to the original 3 board edge connectors. An HP-IB connector is the external interface. This kit had to be installed at the factory, as it requires a modification on the boards of the original tape drive (I am not sure what it is).

My 7970E has the HP-IB option, which allowed me to connect it to an HP-IB equipped PC and my HP-85, as explained below.

HP 7970 Documentation

Interfacing the HP 7970E

Unless you have an original HP 2116, HP 2100 or HP 1000 M/E/F system with the appropriate interface boards pairs (the HP 13181 or HP 13183), interfacing to an HP 7970 tape drive is a challenge. There are no interface boards that plug into a PC that allows you to connect to them. But you might be able to design your own interface with a microcontroller or an FPGA as described below. Also, I was able to connect an HP 7970E equipped with a HP-IB interface to a PC and to my HP-85.

Connecting the HP 7970 A/B/C/E to an HP 1000 computer

The 3-connectors native interface (controller, read, write) is relatively straightforward, although it uses many pins. The protocol is described in this document:

At the other end of the cable, the tape drive connects to a pair of interface boards (pictured below) inside the HP 1000. The board pair product number is HP 13181 for the 7970 A/B/C drives at 800 CPI, and HP 13183 for the HP 7970E at 1600 CPI. One board is labeled MAG TAPE 1, the other MAG TAPE 2, and need to be installed consecutive IO slots. You'll also need the large 13181-60030 interface cable. It has two connectors on one side to hook to the board pair and three on the other to connect inside the tape drive.

HP 13181 Interface Board 1

HP 13181 Interface Board 2

Connecting the HP 7970 A/B/C/E to a PC using the native interface

I don't know of any interface boards that can be used to connect the HP 7970 to a PC using the native parallel interface (however, see below for doing it with the optional HP-IB interface). That said, it should be possible to implement the parallel interface protocol with a microcontroller or an FPGA. For the FPGA, you can inspire yourself of the HP 13181 and HP 13183 interface cards TTL implementation, sunce the schematics are available in the service manuals:

Connecting the HP 7970E to a PC via the HP-IB optional interface

The 7970E has an optional HP-IB interface, and my tape unit came with it. I was able to connect the drive with an old PC equipped with an National Instrument GPIB interface, and use Ansgar Kueckes HPDIR program to talk to it. In fact, this was the first time Ansgar's program was ever tested on a real HP 7970E, and we had to make quite a few tweaks to the program to get it to work properly.

To read the tape, the syntax from a DOS command window is:

hpdir -dup 701: file.tap

This will dump the content of the entire tape in a SIMH-formatted file.tap.

There are quite a few restrictions though: it works only under Windows 98. We were unable to get the timing tight enough under Windows XP. It also only works with one of the older PCI or ISA GPIB cards supported by HPDIR - in particular, it will not work with newer USB based GPIB interfaces.

For the PC running Win98, I used one of my DolchPAC 65 luggable PC for the setup. You can see the working result in the video above starting around 7:08.

Connecting the HP 7970E to an HP-85 via the HP-IB interface

Since my 7970E had the optional HP-IB interface, it seemed natural to interface it to my HP-85. But this turned out to be more challenging than I anticipated :

  • The HP-85 mass storage ROM do not support the HP 7970E
  • The HP-85 is too slow to keep up with the HP 7970E data rate
  • The HP-85 HP-IB implementation differs fundamentally from that of the HP 7970E in its treatment of parity
  • The HP 7970E HP-IB protocol quite is quite complicated and not very clearly documented.

Nevertheless I was able to surmount all four problems. This led to my ASCII art demo setup, where an ASCII art picture is read from a tape on the HP 7970E and printed on a HP 2631G matrix printer, both dwarfing the little HP-85.

The program and details to make this all work are complicated and are described on this page: