M768

This document is a schematic diagram for the digital DELAY TRANSMITTER M768, a proprietary electronic circuit designed by Digital Equipment Corporation for test and maintenance purposes.

The circuit primarily functions as a controller and timing generator, likely for a peripheral device such as a magnetic tape drive, given the presence of signals like "FORWARD," "REVERSE," "WRITE," "READ," "CLOCK," and "TRANSPORT SETTLING DOWN."

Key features and sections of the schematic include:

1. Input Decoding and Selection: A series of input lines (e.g., RD2 through RDØ, SELECT REMOTE L, FORWARD (Ø) H, WRITE ENABLE (Ø) H) are processed by logic gates (E1-E4) and a DEC 8251 integrated circuit to interpret commands and select operational modes.
2. Control Signal Generation (Diode Matrix): Outputs from the DEC 8251 are fed into a diode matrix (D10-D43) which decodes them into various operational control signals, including "REV STOP L," "FOR RD STOP L," "FOR WR STOP L," "FOR WD START L," "REV START L," "FOR RD START L," and "CLOCK L."
3. Timing and Skew Control: Logic gates and transistors (Q14-Q18) process signals like "TRANSPORT SETTLING DOWN L," "DELAY STROBE L," and "WRITE CLOCK L" to generate precise timing and skew control signals (e.g., BSDWN H, BSKEW H, BWRC H, BWRL H, BTUR H), critical for data synchronization.
4. Remote Control and Read Output: A section including "SELECT REMOTE H" and "BEMD L" inputs controls a "READ OUT L" signal, indicating capabilities for remote control and monitoring of read operations.
5. Delay Generation Circuit: A dedicated circuit involving a capacitor (C7) and diodes (D50, D51, D52) generates the "DELAY OUT L" signal, central to the device's "Delay Transmitter" function.
6. Logic Convention: The circuit utilizes negative logic signals, where 'L' (low) represents -3V (active) and 'H' (high) represents 0V (inactive).
7. Component Specifications: Standard components are indicated, with resistors being 1/4W, 5%; transistors are DEC65348; diodes are D664; capacitors are .01uF, 100V, 20%; and ICs are SP384 (unless otherwise specified, such as DEC 8251 and DEC 8281).