DEC PC05 paper tape reader/puncher

Parent Category: Stories Category: Love affair with the DEC paper tape PC05 Written by Administrator

pc05 in rack


The PC05 is the standard device on DEC PDP-11's to read or punch paper tapes. It was used in the 1970's, like most DEC devices of this aera it is mounted into 19" racks.

It needs the PC11 papertape controller (DEC module M7810), which is only available for UNIBUS. QBUS PDP-11's can not use the PC05, they have to use reader/punchers with a serial interface.

In contrast to ASR33 teletypes, it can read at 300 characters per second. An ASR33 can read 10 chars/second, so DEC called the PC05 "High speed". Is this fast? In 2015 there is just one device famous for an even lower transmission speed: the space probe "New Horizons" transmits data at 1 kBit/sec. This is 125 bytes per second  ... from the distance of Pluto. That's one for Randall: "WHAT IF they'd use a 3 billion miles long paper tape instead of radio?"

Also in contrast to ASR33, it PC05 processes paper tape in a "fan fold" manner. DEC folded the paper tape strips, so after read-in they must not be spooled back. Instead after reading a tape the folded paper tape could immediately stored away or put into the reader again. Storage of folded strips was also more handy.

Basic documentation for the PC05 is on bitsavers, but not for all variants. The XXDP diagnostic for PC11/PC05 is "ZPCA".

The PC05 was only made for 115 VAC line voltage.

pc05 power inlet

For the European market, DEC mounted 220V/110V step down transformers to the back door of their rack cabinets.

Usage on other PDP's

The DEC "High speed Papertape Reader and Punch" was used with little modifications on severals DEC computer lines: in PDP-8 (as PC04), in PDP-10 (as PTR/PTP10), in the PDP-11 and PDP-15 as PC05. It was constructed in 1969 (according to the earliest note on the schematics), and several thousands must have been build (check out the serial number on the identification plate shown below). In the 1960's there was also an older PC02.

The construction of the core device was identically for all PDP's, only backplane wiring and module usage differed.

The host PDP can be recognized at the identification plate. The plate contains also the serial number for the host controller, which is "PC15" for PDP-15 in this case.

pc05 label pc11

pc05 label pc15

 Even big machines like the PDP-10 with lot of tape and disk drives were equipped with the slow paper tape reader: 

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One main use for paper tape always was running the MAINDEC diagnostics, which were delivered on paper tape sorted into blue plastic trays (see the one glued onto the PDP-10 in the picture above).

paper tape dec tray


Know your  PC05

The reader and the puncher unit inside the PC05 are two separate devices. They only share the chassis, the flip chip backplane and the power supply.

pc05 top view-Bearbeitet

1 = Power supply.
2 = flip chip wire wrap backplane with electronic modules. There's no interconnection between reader and puncher logic.
3 = reader stepper motor with hold resistors (wasting energy as if it were free).
4 = reader head with lamp, feed wheel, tape depressor and photo transistors to read the paper holes.

pc05 read head old

5 = puncher, made by Roytron. It operates like an electrical typewriter: electric signals drive solenoids, solenoids move small control metal strips, these lock the actual punchers with a rotating wheel, and the punchers are pushed upward through the paper for one rotational period.

pc05 punch roytron

6 = waste container for punched out "chad".
7 = paper tape to be punched.
8 = electronic switch for puncher motor ("triac assy"), invisible here.
9 = reader and punch 40 pin flat cables to UNIBUS PC11 controller.


Logic modules

The PC05 logic consists of these modules (varies with version of PC05):

pc05 modules

M715: "Reader Timing". Generates signals for the stepper motor.

M705/7050: "Reader Control", contains data latch and state machine for the reader.

M710: "Punch Control", contains data latch and state machine for the puncher.

3x M044: power driver for the solenoids in the Roytron puncher. Total of 12 channels, but only 10 are used (the feed hole is driven by two channels)

4x M040: "Solenoid driver", power drivers for the stepper motor. Four phases are driven by two channels each.

G918: Photo amplifier, generates logic signals from the photo transistor array in the reader.

K303: Timeout unit, to be used for puncher motor activation. Only used on older M710.