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MC68336/376
SYSTEM INTEGRATION MODULE
MOTOROLA
USER’S MANUAL
Rev. 15 Oct 2000
5-56
determine port size (8- or 16-bit) for dynamic bus allocation. A pin data register
(PORTC) latches data for chip-select pins that are used for discrete output.
Blocks of addresses are assigned to each chip-select function. Block sizes of two
Kbytes to one Mbyte can be selected by writing values to the appropriate base address
register (CSBAR[0:10] and CSBARBT). Multiple chip-selects assigned to the same
block of addresses must have the same number of wait states. The base address reg-
ister for a chip-select line should be written to a value that is an exact integer multiple
of both the block size and the size of the memory device being selected.
Chip-select option registers (CSORBT and CSOR[0:10]) determine timing of and con-
ditions for assertion of chip-select signals. Eight parameters, including operating
mode, access size, synchronization, and wait state insertion can be specified.
Initialization software usually resides in a peripheral memory device controlled by the
chip-select circuits. A set of special chip-select functions and registers (CSORBT and
CSBARBT) is provided to support bootstrap operation.
Comprehensive address maps and register diagrams are provided in APPENDIX D 5.9.1.1 Chip-Select Pin Assignment Registers
The pin assignment registers contain twelve 2-bit fields that determine the functions of
the chip-select pins. Each pin has two or three possible functions, as shown in Table Table 5-19 shows pin assignment field encoding. Pins that have no discrete output
function must not use the %00 encoding as this will cause the alternate function to be
selected. For instance, %00 for CS0/BR will cause the pin to perform the BR function.
Table 5-18 Chip-Select Pin Functions
Chip-Select
Alternate
Function
Discrete
Output
CSBOOT
—
CS0
BR
—
CS1
BG
—
CS2
BGACK
—
CS3
FC0
PC0
CS4
FC1
PC1
CS5
FC2
PC2
CS6
ADDR19
PC3
CS7
ADDR20
PC4
CS8
ADDR21
PC5
CS9
ADDR22
PC6
CS10
ADDR23
ECLK