Cpu; Memory - Tandy 102 Service Manual

CPU
The CPU is an 80C85A that runs at a clock speed of 2.4576 MHz. It is an 8-bit, parallel Central
Processing Unit using C-MOS technology.- The instruction set is fully compatible with the 8085A
microprocessor. The 80C85A uses a multiplexed data bus. The CPU bus is divided into two
sections- the 8-bit address bus named the A8-A1 5, and the 8-bit address and data bus named the
ADO-AD7. The address bus signals are separated at M1, using the ALE* (Address Latch Enable)
signal.
M20.M21
CPU
A8-415
"
,
M2
ADO-
AD7
RD
ALE
M20
RDA
ALEX
AS -A15
A0-A7
ADO-AD7
M20
Figure 4-3. Functional Block Diagram of Bus Separation Circuit
Memory
The memory of the Tandy 102 consists of a 32 KB standard ROM, three 8 KB C-MOS static RAMs
and a 32 KB optional ROM.
The standard RAMs equipped in the Tandy 102 are M9, M8 and M7. By installing M6, memory
capacity can be increased to 32 KB. The ROM used in the Tandy 102 is a 32 KB (256K bits)
memory.
It is operated only by a +5V power source with an access time of 600 nsec (Max.).
The BASIC program and BIOS program which operate the LCD, printer etc. are stored in the
standard ROM.
An optional ROM can be installed onto the special IC socket by removing the ROM cover on the
bottom case of the Tandy 102. Various types of application programs are stored in the optional
ROM.
0000H
(
32K Byte)
STANDARD
ROM
7FFFH
8000H
OPTION
RAM I
9FFFH ( 8K B te)
AOOOH ST A
RAM 3
BFFFH
(SK
B
to)
COOOH
STANDARD
DFFFH
RAM 2
E000H STANDARD
RAM I
FFFFH
K B t
Figure 4-4. Memory Map
OPTION
BAN K
SELECTION (32K Byte)
-- - - - - -STANDARD
4-3