Texas Instruments 99/4A - Page 45

MEMORY ALLOCATION
The memory address space is broken into 8 blocks of 3K bytes of
memory. The third block (addresses 4000 - 5FFF) is predecoded and
made available at the I/O port for the peripherals. The second
sixth, seventh and eighth blocks (addresses 2000-3FFF and A000 -
FFFF) are available for further expansion. For the speech module,
(addresses 90XX - 94XX), a predecoded line is available at the I/O
port.
TABLE 4 SYSTEM MEMORY MAP
HEX ADDRESS
0 - 1FFF
2000 - 3FFF
4000 - 5FFF
6000 - 7FFF
S000 ~ 9FFF
A000 - BFFF
C000 - DFFF
E000 - FFFF
Console ROM Space
Memory Expansion
Peripheral expansion (predecoded to I/O Connector)
Game cartridge ROM/RAM (predecoded to GROM Connector)
Microprocessor RAM,, VDP, GROM, SOUND and SPEECH select.
Memory Expansion
Memory Expansi on
Memory Expansion
TABLE 5 MEMORY MAPPED DEVICES
ADDRESSES AO Al
A4
8000
8400
8300
8802
8 COO
8C02
9000
9400
9800
9802
9 COO
9C02
1 (j 0
1 0 0
1 (j 0
1 (j 0
1 0 0
1 0 o
1 0 0
1 0 0
1 (j 0
1 0 0
1 0 o
1 (j (j
0 0
o o
0 1
0 1
0 1
0 1
1 0
1 0
1 1
1 1
1 1
1 1
0 0
1 o
0 0
0 1
1 0
1 1
0 0
1 0
0 0
0 1
1 0
1 1
USE
A15
0
Internal RAM
0
(8300 — 83FF)
Sound
(j
VDP Read Data
(j
VDP Read Status
0
VDP Write Data
0
VDP Write
0
Address
Speech Read
0
Speech Write
(j
GROM Read Data
0
GROM Data
0
Address
GROM Write Data
0
GROM Write
Address