Freescale Semiconductor MC68332 - Chip-Select Pin Assignment Registers

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
functions, as shown in Table 4-19.
Table 4-20 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.
Refer to 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 4.8.4 Chip-Select Reset
Operation 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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