The Tektronix 7M13 is a "Readout Unit" that allows the user to enter text into the scope's readout system for that module slot. It is intended to include identifying text and picture numbers for photographic documentation.
A built-in camera counter displays a pre-settable count in the second (lower) readout channel, which can be advanced manually by push-button or automatically through the a camera shutter. The only editing function provided is to overwrite the character just entered (by holding the MODIFY button). To correct other errors, one needs to erase the display field.
|Character positions||2 fields (top, bottom) of 10 characters each|
|Camera counter||0-99, lower field only; ground contact closure input|
Internals and Repair Issues
The 7M13 is relatively simple and robust electrically (consisting mostly of 74xx TTL logic), however, due to the number of switches, there can be electromechanical problems. For example, a 7M13 may appear unresponsive if the camera counter "(P)RESET" button is not fully released.
The 7M13 uses four 7489 TTL 16×4 RAMs to store the characters entered, and four 155-0038-01 Tek-made D/A converter chips to drive the analog row/column readout lines. One RAM and D/A each are assigned to row and column readout signals in each channel, and are addressed by a counter synchronized to the readout time slot pulses. In other words, characters are not stored in ASCII bytes but in row/column pairs matching the readout system's character set. The keyboard is arranged in a matching matrix of double-contact (DPST) keys that generate the row/column coordinates through 74147 priority encoders.