xerox Alto Interfaces Nov78 free download

File name Alto_Interfaces_Nov78.pdf

XEROX PALO ALTO RESEARCH CENTER Computer Science Laboratory April, 1973 - CSL Archieve # 3AL-038 retyped November 7, 1978 To: Alto Group From: C. Thacker Subject: Alto Interfaces This memo is in response to the request for a description of the Alto I/O system. Familiarity with the Alto is assumed 1 . . There are two basic ways in which I/O devices may be connected to the Alto. A device may appear to a program as one or more memory locations in the range 177000-177777, in which case it responds to addresses from MAR, for its selection, and transfers data on the memory data bus, MD(00)'-MD(15)'. Alternatively, a device may connect directly to the processor bus, and be selected by task-specific F1 or F2 signals. The latter interface will usually have its own task microcode, and will be used only for high speed devices (> 1K words/sec). The memory bus interface will usually be used for slow peripherals which can be driven by a "Nova" program, although nothing prohibits mixing the interface methods, i.e., a memory bus device can have its own microcode task. Memory Bus The memory bus signals are: MD(OO)'