
MC68CK338
MC68CK338TS/D
MOTOROLA
61
ILSCI — Interrupt Level of SCI
ILSCI determines the priority of SCI interrupts. This field must be given a value between $0 (interrupts
disabled) to $7 (highest priority).
If ILQSPI and ILSCI are the same nonzero value, and both submodules simultaneously request inter-
rupt service, QSPI has priority.
At reset, QIVR is initialized to $0F, which corresponds to the uninitialized interrupt vector in the excep-
tion table. This vector is selected until QIVR is written. A user-defined vector ($40–$FF) should be writ-
ten to QIVR during QSM initialization.
After initialization, QIVR determines which two vectors in the exception vector table are to be used for
QSM interrupts. The QSPI and SCI submodules have separate interrupt vectors adjacent to each other.
Both submodules use the same interrupt vector with the least significant bit (LSB) determined by the
submodule causing the interrupt.
The value of INTV0 used during an interrupt-acknowledge cycle is supplied by the QSM. During an in-
terrupt-acknowledge cycle, INTV[7:1] are driven on DATA[7:1] IMB lines. DATA0 is negated for an SCI
interrupt and asserted for a QSPI interrupt. Writes to INTV0 have no meaning or effect. Reads of INTV0
return a value of one.
5.4.2 Pin Control Registers
The QSM uses nine pins, eight of which form a parallel port (PORTQS) on the MCU. Although these
pins are used by the serial subsystems, any pin can alternately be assigned as general-purpose I/O on
a pin-by-pin basis.
Pins used for general-purpose I/O must not be assigned to the QSPI by register PQSPAR. To avoid
driving incorrect data, the first byte to be output must be written before DDRQS is configured. DDRQS
must then be written to determine the direction of data flow and to output the value contained in register
PORTQS. Subsequent data for output is written to PORTQS.
PORTQS latches I/O data. Writes drive pins defined as outputs. Reads return data present on the pins.
To avoid driving undefined data, first write a byte to PORTQS, then configure DDRQS.
QIVR —
QSM Interrupt Vector Register
$YFFC05
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
QILR
INTV
RESET:
0
0
0
0
1
1
1
1
PORTQS —
Port QS Data Register
$YFFC14
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
RESERVED
PQS7
PQS6
PQS5
PQS4
PQS3
PQS2
PQS1
PQS0
RESET:
0
0
0
0
0
0
0
0