MC68331CEH16 Datasheet, PDF (35/84 Pages) Freescale Semiconductor, Inc – 32-Bit Modular Microcontroller

Freescale Semiconductor, Inc.
3.6 General-Purpose Input/Output
SIM pins can be configured as two general-purpose I/O ports, E and F. The following paragraphs de-
scribe registers that control the ports.
PORTE0, PORTE1 —Port E Data Register
$YFFA11, $YFFA13
15
8
7
6
5
4
3
2
1
0
NOT USED
PE7 PE6 PE5 PE4 PE3 PE2 PE1 PE0
RESET:
U
U
U
U
U
U
U
U
A write to the port E data register is stored in the internal data latch and, if any port E pin is configured
as an output, the value stored for that bit is driven on the pin. A read of the port E data register returns
the value at the pin only if the pin is configured as a discrete input. Otherwise, the value read is the value
stored in the register.
The port E data register is a single register that can be accessed in two locations. When accessed at
$YFFA11, the register is referred to as PORTE0; when accessed at $YFFA13, the register is referred
to as PORTE1. The register can be read or written at any time. It is unaffected by reset.
DDRE — Port E Data Direction Register
$YFFA15
15
RESET:
NOT USED
8
7
6
5
4
3
2
1
0
DDE7 DDE6 DDE5 DDE4 DDE3 DDE2 DDE1 DDE0
0
0
0
0
0
0
0
0
The bits in this register control the direction of the pin drivers when the pins are configured as I/O. Any
bit in this register set to one configures the corresponding pin as an output. Any bit in this register
cleared to zero configures the corresponding pin as an input. This register can be read or written at any
time.
PEPAR — Port E Pin Assignment Register
$YFFA17
15
8
7
6
5
4
3
2
1
0
RESET:
NOT USED
PEPA7 PEPA6 PEPA5 PEPA4 PEPA3 PEPA2 PEPA1 PEPA0
DATA8 DATA8 DATA8 DATA8 DATA8 DATA8 DATA8 DATA8
The bits in this register control the function of each port E pin. Any bit set to one configures the corre-
sponding pin as a bus control signal, with the function shown in the following table. Any bit cleared to
zero defines the corresponding pin to be an I/O pin, controlled by PORTE and DDRE.
Data bus bit 8 controls the state of this register following reset. If DATA8 is set to one during reset, the
register is set to $FF, which defines all port E pins as bus control signals. If DATA8 is cleared to zero
during reset, this register is set to $00, configuring all port E pins as I/O pins.
Any bit cleared to zero defines the corresponding pin to be an I/O pin. Any bit set to one defines the
corresponding pin to be a bus control signal.
Table 16 Port E Pin Assignments
PEPAR Bit
PEPA7
PEPA6
PEPA5
PEPA4
PEPA3
PEPA2
PEPA1
PEPA0
Port E Signal
PE7
PE6
PE5
PE4
PE3
PE2
PE1
PE0
Bus Control Signal
SIZ1
SIZ0
AS
DS
RMC
AVEC
DSACK1
DSACK0
MC68331TS/D
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