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MPC555
/
MPC556
MODULAR INPUT/OUTPUT SUBSYSTEM (MIOS1)
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
15-24
6
FORCB
Force B. In the OCB, OCAB and OPWM modes, the FORCB bit allows the software to force the
output flip-flop to behave as if a successful comparison had occurred on channel B (except that
the FLAG line is not activated). Writing a one to FORCB resets the output flip-flop; writing a zero
to it has no effect.
In the DIS, IPWM, IPM and IC modes, the FORCB bit is not used and writing to it has no effect.
FORCB is cleared by reset and is always read as zero. Writing a one to both FORCA and
FORCB simultaneously resets the output flip-flop.
7:8
—
Reserved
9:10
BSL
Bus select.These bits are used to select which of the four possible 16-bit counter bus passing
nearby is used by the MDASM. Refer to
to see how the MDASM is connected to
the 16-bit counter buses in the MIOS1.
NOTE
: In the MPC555 / MPC556, only 0b00 (CB6) and 0b01 (CB22) are implemented.
11
—
0
12:15
MOD
Mode select. These four mode select bits select the mode of operation of the MDASM. To avoid
spurious interrupts, it is recommended that MDASM interrupts are disabled before changing the
operating mode. It is also imperative to go through the disable mode before changing the oper-
ating mode. See
for details.
Table 15-18 MDASM Mode Selects
MDASM Control Register Bits
Bits of
Resolution
Counter
Bus Bits
Ignored
MDASM Mode of Operation
MOD
0000
—
—
DIS – Disabled
0001
16
—
IPWM – Input pulse width measurement
0010
16
—
IPM – Input period measurement
0011
16
—
IC – Input capture
0100
16
—
OCB – Output compare, flag on B compare
0101
16
—
OCAB – Output compare, flag on A and B compare
0110
—
—
Reserved
0111
—
—
Reserved
1000
16
—
OPWM – Output pulse width modulation
1001
15
0
OPWM – Output pulse width modulation
1010
14
0,1
OPWM – Output pulse width modulation
1011
13
0-2
OPWM – Output pulse width modulation
1100
12
0-3
OPWM – Output pulse width modulation
1101
11
0-4
OPWM – Output pulse width modulation
1110
9
0-6
OPWM – Output pulse width modulation
1111
7
0-8
OPWM – Output pulse width modulation
Table 15-17 MDASMSCR Bit Descriptions (Continued)
Bit(s)
Name
Description
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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