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17.9.1.1 MDASM Signal Functions
The MDASM has one dedicated external signal. This signal is used in input or in output
depending on the selected mode. When in input, it allows the MDASM to perform input
capture, input pulse width measurement and input period measurement. When in output, it
allows output compare, single shot output pulse, single output compare and output port bit
operations as well as output pulse width modulation.
In disable mode, the signal becomes a high impedance input
and the input level on this signal is reflected by the state of the
PIN bit in the MDASMSCR register.
17.9.2
MDASM Description
The MDASM contains two timing channels A and B associated with the same input/output
signal. The dual action submodule is so called because its timing channel configuration
allows two events (input capture or output compare) to occur before software intervention
is required.
Six operating modes allow the software to use the MDASM's input capture and output
compare functions to perform pulse width measurement, period measurement, single pulse
generation and continuous pulse width generation, as well as standard input capture and
output compare. The MDASM can also work as a single I/O signal. See Table 17-17 for
details.
Channel A comprises one 16-bit data register and one 16-bit comparator. Channel B also
consists of one 16-bit data register and one 16-bit comparator, however, internally, channel
B has two data registers B1 and B2, and the operating mode determines which register is
accessed by the software:
• In the input modes (IPWM, IPM and IC), registers A and B2 are used to hold the
captured values; in these modes, the B1 register is used as a temporary latch for
channel B.
• In the output compare modes (OCB and OCAB), registers A and B2 are used to
define the output pulse; register B1 is not used in these modes.
• In the output pulse width modulation mode (OPWM), registers A and B1 are used
as primary registers and hidden register B2 is used as a double buffer for channel B.
Register contents are always transferred automatically at the correct time so that the
minimum pulse (measurement or generation) is just one 16-bit counter bus count. The A
and B data registers are always read/write registers, accessible via the MIOB.
In the input modes, the edge detect circuitry triggers a capture whenever a rising or falling
edge (as defined by the EDPOL bit) is applied to the input signal. The signal on the input
signal is Schmitt triggered and synchronized with the MIOS14 CLOCK.
MOTOROLA
Chapter 17. Modular Input/Output Subsystem (MIOS14)
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
MIOS14 Double Action Submodule (MDASM)
NOTE
17-27
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