SYSTEM INTEGRATION MODULE
MC68332
4-52
USER’S MANUAL
4.8.1.1 Chip-Select Pin Assignment Registers
The pin assignment registers contain twelve 2-bit fields (CS[10:0] and CSBOOT) that
determine the functions of the chip-select pins. Each pin has two or three possible
.
shows pin assignment field encoding. Pins that have no discrete output
function do not use the %00 encoding.
Port size determines the way in which bus transfers to an external address are allo-
cated. Port size of eight bits or sixteen bits can be selected when a pin is assigned as
a chip select. Port size and transfer size affect how the chip-select signal is asserted.
4.8.1.3 Chip-Select Option Registers
for more information.
Out of reset, chip-select pin function is determined by the logic level on a correspond-
ing data bus pin. These pins have weak internal pull-up drivers, but can be held low
by external devices. (Refer to
4.6.3.1 Data Bus Mode Selection
for more informa-
tion.) Either 16-bit chip-select function (%11) or alternate function (%01) can be select-
ed during reset. All pins except the boot ROM select pin (CSBOOT) are disabled out
of reset. There are twelve chip-select functions and only eight associated data bus
pins. There is not a one-to-one correspondence. Refer to
for more detailed information.
The CSBOOT signal is normally enabled out of reset. The state of the DATA0 line dur-
ing reset determines what port width CSBOOT uses. If DATA0 is held high (either by
the weak internal pull-up driver or by an external pull-up device), 16-bit width is select-
ed. If DATA0 is held low, 8-bit port size is selected.
Table 4-19 Chip-Select Pin Functions
16-Bit
Chip Select
8-Bit
Chip Select
Alternate
Function
Discrete Output
CSBOOT
CSBOOT
CSBOOT
—
CS0
CS0
BR
—
CS1
CS1
BG
—
CS2
CS2
BGACK
—
CS3
CS3
FC0
PC0
CS4
CS4
FC1
PC1
CS5
CS5
FC2
PC2
CS6
CS6
ADDR19
PC3
CS7
CS7
ADDR20
PC4
CS8
CS8
ADDR21
PC5
CS9
CS9
ADDR22
PC6
CS10
CS10
ADDR23
ECLK
Table 4-20 Pin Assignment Field Encoding
Bit Field
Description
00
Discrete Output
01
Alternate Function
10
Chip Select (8-Bit Port)
11
Chip Select (16-Bit Port)
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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