Opcode Changes

The IOS instruction was consistent between 1957 and 1963. Its opcode was 04, sometimes known as OPR, and apparently also used for the AOP instruction.

The AOP instruction provided for operations entirely within the Ariothmetic Element (with no memory reference). It provided for encoding the operation to be performed within the base address portion of the instruction word. However, none of the documentation we have found to date explains what these operations were or what they did.

1957

I/O instruction opcodes were RDN, RDS, IOS.

IOS provided for connecting and disconnecting peripherals. RDS and RDN performed I/O reads or writed, depending on the mode of the relevant device.

Opcode	Function	Operand Bits Transferred	Comment
RDN	I/O read or write	Least-significant 6 bits	Analogous to TSD’s “normal” mode for, say, the paper tape reader.
RDS	I/O read or write	Transfers every sixth bit, and then shifts word one bit leftward	Analogous to the later “Assembly” mode of, say, the paper tape reader.
IOS	I/O control	Operand specifies the operation to be performed, of the device mode to set

For details, see “The Lincoln TX-2 Input-Output System” by James W Forgie, Lincoln Lab memo 6M-4968.

1963

I/O instruction opcodes were TSD, IOS (see the Users Handbook [Vanderburgh61]). The splay (“assembly”) and shifting behaviours still existed, but were selected differently. The RDN/RDS opcodes are replaced by a single TSD opcode.

Opcode	Function	Comment
TSD	I/O Read or write	Normal/Assembly bit distribution and shifting now depends on the mode setting of the device. Sequences 0, 76, and 77 always perform a shift on TSD. Sequence 75 never does.
IOS	I/O control	Appears similar to the 1957 description.

For details, see the TX-2 Users Handbook.