Keyboard; Memory Controller Circuit - HP 743 Service Handbook

Keyboard

A keyboard must be connected to either the PS/2 0 or PS/2 1 port if graphics are used as
part of the console path. When a graphics device is specified as the console path, the boot
ROM first checks for a keyboard using the keyboard search list. If the system does not find
a keyboard as part of the console path, graphics will not be enabled.

Memory Controller Circuit

Memory is managed by the CPU's memory controller circuit. You can install up to 256
Mbytes of RAM. An Error Checking and Correcting (ECC) function checks memory word
read/write operations and detects both single-bit and double-bit errors. If the ECC detects
a single-bit error, it will be corrected. Double-bit errors are detected but not corrected. Tri-
ple and quadruple bit errors are grouped in nybbles, using a 64-bit memory bus.
The Model 743 uses two RAM card locations. RAM stacks are labeled on the system
board as:
• RAM stack 1, located behind the PS/2 (mouse and keyboard) connectors, supports
up to three RAM cards. The physical RAM slot positions are:
Bottom RAM card, slot 0
Middle RAM card, slot 1
Top RAM card, slot 2
• RAM stack 2, located behind the audio connectors supports only one RAM card
and is in physical RAM slot 4.
Functional Description
Overview
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