Motorola MPC860 PowerQUICC User Manual page 624

Part V. The Communications Processor Module
21.3 NMSI ConÞguration
The SI supports a non-multiplexed serial interface (NMSI) mode for the SCCs and SMCs.
The decision of whether to connect the SCCs to the NMSI is made in the SICR; the SMCs
are connected through SIMODE. An SCC or SMC can be connected to the NMSI,
regardless of the other channels connected to a TDM channel. However, NMSI pins can be
multiplexed with other functions at the parallel I/O lines. Therefore, if a combination of
TDM and NMSI channels are used, the decision of which SCC and SMC to connect and
where to connect them should be made by consulting the pinout in Chapter 3, ÒHardware
Interface Overview.Ó
The clocks that are provided to the SCCs and SMCs are derived from four internal baud
rate generators and eight external CLK pins. There are two main advantages to this
bank-of-clocks approach. First, an SCC or SMC is not forced to choose its clock from a
predeÞned pin or baud rate generator. Second, if a group of SCC receivers and transmitters
need the same clock rate they can share the same pin, leaving other pins available other
functions and minimizing the potential skew between multiple clock sources.
The baud rate generators also make their clocks available to external logic, regardless of
whether the BRGs are being used by an SCC or SMC. The BRGOn pins are multiplexed
with other functions, so all BRGOn pins may not always be available. See Chapter 3,
ÒHardware Interface Overview.Ó
The following restrictions apply to the bank-of-clocks mapping:
¥ Only eight of the twelve clock sources can be connected to a given SCC receiver or
transmitter.
¥ The SMC transmitter must have the same clock source as the receiver when
connected to the NMSI.
Once the clock source is selected, the clock is given an internal name. For the SCCs, the
name is RCLKx and TCLKx and for the SMCs, the name is simply SMCLKx. These
internal names are used only in NMSI mode to specify the clock that is sent to the SCC or
SMC. These names do not correspond to physical pins on the MPC860. Note the internal
RCLKx and TCLKx can be used as inputs to the DPLL unit, which is inside the SCCx; thus,
RCLKx and TCLKx are not always required to reßect the actual bit rate on the line.
The signals available to each SCC and SMC in NMSI mode are shown in Figure 21-28.
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