Light Duty Card Reader

The CRO1 is a PDP-X Technical Memorandum #7 describing a light-duty card reader designed around the NCR Type EM-D2 mechanical reader. It operates at a maximum rate of 100, 80-column cards per minute, reading one column every 7 milliseconds, with approximately 25 milliseconds between cards.

The reader supports two modes:

1. Binary Mode: Each column is read as a 12-bit binary number, with specific rows (9 and 12) mapped to low and high order bit positions, respectively, indicating the presence or absence of a punch (1=punch, 0=no punch).
2. Alphanumeric Mode: Rows 1-9 are encoded into a 4-bit BCD set (low order), while rows 10, 11, and 12 are encoded into two high-order bits based on zone punches.

Programming the CRO1 involves loading and manipulating its status register using specific Input/Output (IO) instructions (IOC, IOX, IOS, IOT). The status register contains critical bits such as NOT READY (indicating conditions like power off or no card), BIN (to select binary or alphanumeric mode), CARD DONE, REQ, BUSY, LOW, and ENABLE. Interrupts are generated based on the status of these bits, allowing for central processor control transfer to a service routine or data transfer to memory via a multiplexor channel.

Operator controls include an ON/OFF switch, an AUTO/MAN switch (for automatic program control or manual feed), a REG key (to manually feed the first card), and a SKIP switch (to clear the NOT READY bit). Data transfer is typically handled by the multiplexor channel, with provisions for handling channel overflows and card completion. For direct Hollerith to ASCII translation on a per-column basis, the document suggests using a custom routine with table lookup, rather than the multiplexor channel mode.