MC68331
USER’S MANUAL
REGISTER SUMMARY
MOTOROLA
D-23
D
D.3.25 CSBARBT
— Chip Select Base Address Register Boot ROM
CSBAR[0:10]
— Chip Select Base Address Registers
$YFFA48
$YFFA4C–$YFFA74
Each chip-select pin has an associated base address register. A base address is the
lowest address in the block of addresses enabled by a chip select. CSBARBT contains
the base address for selection of a bootstrap peripheral memory device. Bit and field
definition for CSBARBT and CSBAR[0:10] are the same, but reset block sizes differ.
ADDR[23:11] — Base Address
This field sets the starting address of a particular address space.
BLKSZ — Block Size
This field determines the size of the block above the base address that is enabled by
the chip select.
D.3.26 CSORBT
— Chip Select Option Register Boot ROM
CSOR[0:10]
— Chip Select Option Registers
$YFFA4A
$YFFA4E–$YFFA76
Contain parameters that support bootstrap operations from peripheral memory devic-
es. Bit and field definitions for CSORBT and CSOR[0:10] are the same.
MODE — Asynchronous Bus/Synchronous E-clock Mode
Synchronous mode cannot be used with internally generated autovectors.
0 = Asynchronous mode selected
1 = Synchronous mode selected
BYTE — Upper/Lower Byte Option
The value in this field determines whether a select signal can be asserted.
15
14
13
12
11
10
9
8
7
6
5
4
3
2
0
ADDR
23
ADDR
22
ADDR
21
ADDR
20
ADDR
19
ADDR
18
ADDR
17
ADDR
16
ADDR
15
ADDR
14
ADDR
13
ADDR
12
ADDR
11
BLKSZ
RESET:
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Table D-11 Block Size Encoding
BLKSZ[2:0]
000
001
010
011
100
101
110
111
Block Size
2 K
8 K
16 K
64 K
128 K
256 K
512 K
1 M
Address Lines Compared
ADDR[23:11]
ADDR[23:13]
ADDR[23:14]
ADDR[23:16]
ADDR[23:17]
ADDR[23:18]
ADDR[23:19]
ADDR[23:20]
15
14
13
12
11
10
9
6
5
4
3
1
0
MODE
BYTE
R/W
STRB
DSACK
SPACE
IPL
AVEC
RESET:
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0