6.2.2 QSM Pin Control Registers
The QSM uses nine pins. Eight of the pins can be used for serial communication or for
parallel I/O. Clearing a bit in the port QS pin assignment register (PQSPAR) assigns
the corresponding pin to general-purpose I/O; setting a bit assigns the pin to the QSPI.
PQSPAR does not affect operation of the SCI.
The port QS data direction register (DDRQS) determines whether pins are inputs or
outputs. Clearing a bit makes the corresponding pin an input; setting a bit makes the
pin an output. DDRQS affects both QSPI function and I/O function. DDQS1 deter-
mines the direction of the TXD pin only when the SCI transmitter is disabled. When the
SCI transmitter is enabled, the TXD pin is an output. PQSPAR and DDRQS are 8-bit
registers located at the same word address. Table 6-1 is a summary of QSM pin func-
tions.
The port QS data register (PORTQS) latches I/O data. Writes to PORTQS drive pins
defined as outputs. PORTQS reads return data present on the pins when the read is
made. To avoid driving undefined data, first write PORTQS, then configure DDRQS.
Table 6-1 QSM Pin Function
6
QSM Pin
Mode
DDRQS Bit
Bit
State
Pin Function
MISO
Master
DDQS0
0
1
Serial Data Input to QSPI
Disables Data Input
Slave
Master
Slave
0
Disables Data Output
Serial Data Output from QSPI
Disables Data Output
Serial Data Output from QSPI
Serial Data Input to QSPI
Disables Data Input
1
MOSI
DDQS1
DDQS2
0
1
0
1
1
SCK
Master
Slave
0
Disables Clock Output
Clock Output from QSPI
Clock Input to QSPI
1
0
1
Disables Clock Input
Assertion Causes Mode Fault
Chip-Select Output
PCS0/SS
PCS[3:1]
Master
Slave
DDQS3
0
1
0
QSPI Slave Select Input
Disables Select Input
Disables Chip-Select Output
Chip-Select Output
1
Master
Slave
DDQS[4:6]
0
1
0
Inactive
1
Inactive
2
TXD
Transmit
Receive
DDQS7
None
X
NA
Serial Data Output from SCI
Serial Data Input to SCI
RXD
1. PQS2 is a digital I/O pin unless the SPI is enabled (SPE in SPCR1 set), in which case it becomes the SPI
serial clock SCK.
2. PQS7 is a digital I/O pin unless the SCI transmitter is enabled (TE in SCCR1 set), in which case it becomes
SCI serial output TXD and DDRQS has no effect.
MOTOROLA
6-4
QUEUED SERIAL MODULE
MC68331
USER’S MANUAL
MOTOROLA [ MOTOROLA ]
