MC68F375
CONFIGURABLE TIMER MODULE (CTM9)
MOTOROLA
REFERENCE MANUAL
Rev. 25 June 03
13-13
Table 13-5 MCSMSIC Bit Settings
Bit(s)
Name
Description
15
COF
Counter overflow flag. This status flag bit indicates whether or not a counter overflow has oc-
curred. An overflow of the MCSM counter is defined to be the transition of the counter from
0xFFFF to 0xxxxx, where 0xxxxx is the value contained in the modulus latch. If the IL field is
non-zero, an interrupt request is generated when the COF bit is set. This flag bit is set only by
the hardware and cleared only by the software or by a system reset. To clear the flag, the soft-
ware must first read the bit (as ‘1’) then write a ‘0’ to the bit. The flag clearing mechanism will
work only if no flag setting event occurs between the read and write operations; if a COF setting
event occurs between the read and write operations, the COF bit will not be cleared.
0 = Counter overflow has not occurred
1 = Counter overflow has occurred.
14:12
IL[2:0]
Interrupt level. The three interrupt level bits are read/write control bits that select the priority level
of interrupt requests made by the MCSM. These bits can be read or written at any time and are
cleared by reset.
000 = Interrupt disabled.
001 = Interrupt level 1 (lowest).
010 = Interrupt level 2.
011 = Interrupt level 3.
100 = Interrupt level 4.
101 = Interrupt level 5.
110 = Interrupt level 6.
111 = Interrupt level 7 (highest).
11
IARB3
Interrupt arbitration bit 3. The read/write IARB3 bit works in conjunction with the IARB[2:0] field
in the BIUSM module configuration register. Each module that generates interrupt requests on
the IMB must have a unique value in the arbitration field (IARB). This interrupt arbitration iden-
tification number is used to arbitrate for the IMB when modules generate simultaneous interrupts
of the same priority.
10
—
Reserved
9:8
DRV{A:B]
Drive time base bus. DRVA and DRVB are read/write bits that control the connection of the
MCSM to the time base buses A and B.
00 = Neither time base bus A nor time base bus B is driven.
01 = Time base bus B is driven.
10 = Time base bus A is driven.
11 = Both time base bus A and time base bus B are driven.
7IN2
Clock input pin status. This read-only status bit reflects the logic state of the clock input pin CT-
MC. Writing a 0 or 1 to this bit has no effect. Reset has no effect on this bit.
6IN1
Modulus load input pin status. This read-only status bit reflects the logic state of the modulus
load input pin CTML. Writing a 0 or 1 to this bit has no effect. Reset has no effect on this bit.
5:4
EDGEN,
EDGEP
Modulus load edge sensitivity. These read/write bits select the sensitivity of the edge detection
circuitry on the modulus load pin CTML.
00 = None
01 = Positive edge only.
10 = Negative edge only.
11 = Positive and negative edge.
3—
Reserved
2:0
CLK[2:0]
Counter clock select. These read/write control bits select one of six internal clock signals
(PCLKx) or one of two external conditions on the input pin (rising edges or falling edges). The
maximum frequency of the external clock signals is fSYS/4.
000 = Prescaler output 1 (/2 or /3).
001 = Prescaler output 2 (/4 or /6).
010 = Prescaler output 3 (/8 or /12).
011 = Prescaler output 4 (/16 or /24).
100 = Prescaler output 5 (/32 or /48).
101 = Prescaler output 6 (/64 to /768).
110 = CTMC pin input, negative edge.
111 = CTMC pin input, positive edge.
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Freescale Semiconductor, Inc.
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