15

0

3

54

15

0

TMS34094

ISA BUS INTERFACE

SPVS006A – FEBRUARY 1992 – REVISED JUNE 1992

POST OFFICE BOX 1443

13

BASE0–BASE3

Base Address

RESERVED

Base Size

Base Address is used in the memory mapped mode. Each register may contain a value which is compared

against the address bits on the ISA bus. The address comparison is left aligned, the most significant ISA address

(LA23) is compared against the most significant bit in Base Address and so on. When a match occurs, the

corresponding memory map is selected, providing that it is enabled by the corresponding bit in BE3–BE0. The

number of bits used for the actual comparison depends on the Base Size declared. Base Address 0, 1, and 2

are uninitialized at reset. Base Address 3 is set to 0C0h at reset so that BASE3 points to ISA bus physical

address 0C0000h.

Base Size indicates the number of bits from Base Address that should be used to compare against incoming

ISA addresses. Base Size 0, 1, and 2 are uninitialized at reset. Base Size 3 is set to 1h so that BASE3 represents

a 16K-byte window.

BASE SIZE

SEGMENT SIZE

ISA ADDRESS

BITS USED FOR

COMPARISON

BASE ADDRESS

BITS USED FOR

COMPARISON

MAP ADDRESS

BITS USED FOR

TMS34020 LOCAL

MEMORY ADDRESS

0000b

0001b

0010b

0011b

0100b

0101b

0110b

0111b

1000b

1001b

All others

8K

16 K

32 K

64 K

128 K

256 K

512 K

1M

2M

4M

Undefined

LA23–17, SA19–13

LA23–17, SA19–14

LA23–17, SA19–15

LA23–17, SA19–16

LA23–17, SA19–17

LA23–18, SA19–18

LA23–19, SA19

LA23–20

LA23–21

LA23–22

Undefined

Base Address 10-0

Base Address 10-1

Base Address 10-2

Base Address 10-3

Base Address 10-4

Base Address 10-5

Base Address 10-6

Base Address 10-7

Base Address 10-8

Base Address 10-9

Undefined

Map Address 15-0

Map Address 15-1

Map Address 15-2

Map Address 15-3

Map Address 15-4

Map Address 15-5

Map Address 15-6

Map Address 15-7

Map Address 15-8

Map Address 15-9

Undefined

Bit 4 of each BASEx register is reserved. When writing to these registers, write this bit as a zero.

MAP0–MAP3

Map Address

Each MAPx register contains a 16-bit value which acts as a pointer into a segment of the TMS34020 local

memory. The number of bits used as the most significant part of the host address presented to the TMS34020

is determined by the BASE SIZE field in the corresponding base address register. From 6 to 16 of the most

significant bits of the Map Address value will be used, with the ISA address bits providing the lower order address

bits. At reset, MAP0–MAP2 are uninitialized and MAP3 is set to 0F000h.