Functional Description; Introduction; The Memory Management Ic (Memic, 1Lh7) - HP 82718A Service Manual

Section 3
Functional Description
3-1. Introduction
This section gives you a brief functional description of the major blocks in the HP 82718A Expansion Pod.
Refer to the system block diagram shown in figure 3-1.
r H
ute
RON
UJ5
SYSTEM ROM
POMER
SUPPLY
IlKl
U19
ROM
1LJ5
(I)
(111
U17
1LH7
MEMORT
ONTRDUER
TV
U20-27
RAH
64K
ELECTRONIC
DISC
U28
ULE
MODEM
OKTROLLER
MODEM INTERFACE
DATA SIGNALS
CONTROL SIGNALS
ADDRESSES ARE MULTIPLEXED
ON THE OAIA BUS.
64K IS MAXIMUM POSSIBLE
IT IS NOT ALNAYS INSTALLED
SUPPLIES PONER TO THE HP-75.
ALSO .
MAKE-dP
ciRcjir
630 1
CPU
7T
Figure 3-1. HP 82718A Block Diagram
3-2. The Memory Management IC (MEMIC, 1LH7)
Memory Manager 1LH7 (U17) provides the general interface between the HP-75 bus, and the external
memory and modem controller in the pod.
The input to U17 comes from the HP-75 8-bit time-multiplexed address/data bus. Output to the HP-75 is
placed on the HP-75 bus by U17. Six control lines are used to indicate the type of information being
transmitted on the bus and when it is available.
U17 outputs read/write, chip enable, and address signals to the pod allowing one of eight possible RAM
ICs, or the modem to be accessed. Data is transferred to and from the RAMs and the modem on the 8-bit
U17 bus.
A global-disable signal, pin 2, can be tied high to isolate U17 from the bus for troubleshooting.