View source for KW11-W Watchdog Timer

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 [[DEC card form factor|dual]] card, the M7823, along with two standard single card [[FLIP CHIP]]s, an [[M105 Address Selector]] and an [[M782 Interrupt Control|M7821 Interrupt Control]]; they all plugged into an [[Small Peripheral Controller|SPC]] slot.

==Registers==

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

{| border=1
! 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)===
{{16bit-header}}
| ''SLP'' || ''RF'' || colspan=5 | Unused || '''CRF''' || ''SC'' || EI || colspan=4 | Unused || '''ET''' || '''ST'''
{{16bit-bitout}}

* 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)===
{{16bit-header}}
| ''ED15'' || colspan=7 | Unused || ''ED7'' || colspan=7 | Unused
{{16bit-bitout}}

* ED - External Device Status

===Switch Relay Register (WDSRR)===
{{16bit-header}}
| colspan=15 | Unused || '''EOR'''
{{16bit-bitout}}

* EOR - Energize Output Relay

==Eternal links==

* [http://www.bitsavers.org/pdf/dec/unibus/KW11-W_schem_Jul74.pdf KW11-W engineering drawings]

[[Category: UNIBUS Peripherals]]