MOTOROLA
Chapter 18. Peripheral Pin Multiplexing (PPM) Module
18-9
Functional Description
PPM_TCLK settings.
18.3.2
PPM Signal Short Functionality
The MPC561/MPC563 devices have many modules that multiplex their functions onto
shared signals. In order to access those functions, the signals must be configured
appropriately. However, choosing one function can be at the cost of another function. The
PPM makes more functions available simultaneously by creating internal shorts that can
activate functions that would otherwise require an external signal. Internal signal shorts are
enabled using the PPM short register, SHORT_REG.
18.3.2.1 TouCAN Shorting
There are three TouCAN modules on the MPC561/MPC563 devices. Using the PPM it is
possible to internally short the CNRX0 and CNTX0 signals of these three modules to
increase
message
buffer
capacity.
Three
bits
of
the
SHORT_REG
register
(SH_TCAN[0:2]), are allocated to enable four combinations of shorting between the
TouCAN modules. See
Table 18-8 for information on these bit descriptions.
When one TouCAN module is shorted to another, the CANRX signals and the CANTX
signals of both modules are shorted internally. Both modules continue to operate as normal
but all transmit and receive operations are done using only one pair of CANRX and
CANTX signals. The CANRX and CANTX signals of the other module are no longer under
the control of the TouCAN module.
The C_TouCAN signals C_CNTX0 and C_CNRX0 are multiplexed signals. When
C_TouCAN is shorted with one or two other TouCAN modules, C_TouCAN no longer has
control of these signals and so they can be configured for another of the available functions.
18.3.2.2 TPU Shorting
There are two TPU3 modules on the MPC561/MPC563 devices. Using the PPM, it is
possible to internally short channel A_TPUCH0 with B_TPUCH0 and channel
A_TPUCH1 with B_TPUCH1. Two bits of the SHORT_CH register (SH_TPU[1:0])
control the internal shorting. The input/output enable states of the TPU channels
themselves determine the effect that the short bits have on the TPU modules’ operation. See
Table 18-9 for information on SHORT_CH[SH_TPU] bit descriptions.
The PPM only controls the internal shorting of TPU3 channels TPUCH0 and TPUCH1.
TPU channels are configured for input and output by the TPU ROM functions defined for
Figure 18-25. If TPU_A and TPU_B channel 0 are shorted via SHORT_CH[SH_TPU] and
one is set to ouput while the other is set to input, then the data from the output channel will