View source for KW11-L Line Time Clock

[[Image:M787-KW11-L.jpg|300px|thumb|right|KW11-L card]]

The '''KW11-L Line Time Clock''' is a [[UNIBUS]] [[device]] option which provides a [[line time clock]], producing [[interrupt]]s at a rate of 50 or 60 Hz, driven from the [[alternating current|AC]] power provided to the [[Central Processing Unit|CPU]]'s [[power supply]].

The programming interface is extremely simple; there is one [[register]], with two [[bit]]s; one to enable interrupts, and one which is set for every clock cycle (and causes an interrupt when that happens, if the other bit is set).

Physically, the original KW11-L is an [[DEC card form factor|extended-length]] single-height board ('''M787'''), which plugs into a dedicated slot in the CPU's [[backplane]]. Only the [[PDP-11/20]], [[PDP-11/40]], [[PDP-11/45]] and [[PDP-11/70]] support the original card, although later [[PDP-11]]'s generally provided a [[program compatible]] equivalent. E.g. on later UNIBUS machines (e.g. the [[PDP-11/04]] and [[PDP-11/34]]), the functionality was included in the [[DL11-W asynchronous serial line interface|DL11-W]].

[[Category: UNIBUS Peripherals]]