KW11-W Watchdog Timer

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The KW11-W Watchdog Timer is a UNIBUS peripheral which monitors correct operation of a system; unless it is regularly updated by the system's software, it will force a high-priority interrupt.

Physically, the KW11-W was a dual card, the M7823, along with two standard single card FLIP CHIPs, an M105 Address Selector and an M7821 Interrupt Control; they all plugged into an SPC slot.

Registers

The programming interface is fairly simple; there are four registers, which can be configured to any four sequential word locations in the I/O page

Register Abbreviation Address
Watchdog Control and Status Register WDCSR 772400
Clear Flags Register WDCFR 772402
External Control and Status Register WDECSR 772404
Switch Relay Register WDSRR 772406

In the register contents (below), bits which are read/write or unused are shown in normal font, those which are read-only are in italics, and those which are write-only are in bold.

Control and Status Register (WDCSR)

SLP RF Unused CRF SC EI Unused ET ST
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00
  • SLP - Short Loop
  • RF - Receive Flag
  • CRF - Clear Receive Flag
  • SC - Second Chance
  • EI - Enable Interrupts
  • ET - Enable Timer
  • SR - Start Timer

External Control and Status Register (WDECSR)

ED15 Unused ED7 Unused
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00
  • ED - External Device Status

Switch Relay Register (WDSRR)

Unused EOR
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00
  • EOR - Energize Output Relay