The Read Device Reverse (RDR) can be issued only
to magnetic tape. The instruction:
4(1), INPT + 79, INPT
causes the magnetic tape to be moved in a reverse
direction. The first byte read is placed in INPT+79
(HSM 1079), the second byte is placed in INPT+78,
etc., and the last byte read is placed in INPT (HSM
1000). Note that the addresses had to be reversed.
Once staticized and accepted by the channel Control
Electronics, I/O instructions are executed in a si-
multaneous manner, leaving the processor free to
staticize the next instruction in sequence.
The 70/15 Read Auxiliary instruction (RDA) is recog-
nized and executed on the 70/25 as a Read Device
Forward, and does not initiate an Operation Code
Notice that both the RDF and RDR instructions are
Reaching a gap on magnetic tape or reading one
Reading the amount of data specified by the ad-
The Write instruction (WR) transfers data from HSM
to the selected device.
3(1), OUTP, OUTP + 79
prints the contents of HSM 1200-1279 (OUTP area)
to the Printer. Base addresses are implied.
The same command with channel number changed:
4(1), OUTP, OUTP + 79
writes a block of eighty bytes to tape 1 on channel 4, or
2(1), OUTP, OUTP + 79
punches a card.
The Erase (WRE) instruction is a Write command;
however, it can only erase a section of magnetic tape.
4(2), OUTP, OUTP + 50
erases an area oftape equal to the length of 51 bytes.
CONTROLLING PERIPHERAL DEVICES
The instructions discussed above serve the function
of moving data in and out of HSM. The Write Control
(WRC) command has the function of communicating
control information (rewind tape, paper
pocket select, etc.) to a specific device. The instruc-
tion transmits a byte from HSM to the Control Elec-
tronics of the selected device. The bit configurations
of these control bytes are illustrated below.
CARD READER Control Byte
Select Output Stacker #1
Select Output Stacker #2
MAGNETIC TAPE Control Byte
Unwind one gap
Rewind one gap
Rewind and Disconnect
Unload without Rewind (cartridge Tape
Rewind to BT Marker