Motorola MPC533 Reference Manual page 808

Functional Description
18.3.1.3 PPM Control Settings
As data is transferred through the PPM module it must be sampled at a rate which
guarantees its validity. This sample rate is a multiple of PPM_TCLK and is defined by the
SAMP[0:2] field of the PPMPCR register. For transmit operations, the sample rate is the
rate at which TX_DATA receives data from the internal modules. For receive operations, it
is the rate at which the internal modules read RX_SHIFTER. The register RX_DATA is
updated from RX_SHIFTER on complete receive (PPM_TSYNC) cycles.
SYSCLK
PPM_TCLK(1)
Update(1)
SYSCLK
PPM_TCLK(2)
Update(2)
Update(3)
Update(4)
PPM_TCLK(1) = SYSCLK/4
Update(1) every PPM_TCLK(1)clock
PPM_TCLK(2) = SYSCLK/2
Update(2) every PPM_TCLK(2) clock
Update(3) every second PPM_TCLK(2) clock
Update(4) every fourth PPM_TCLK(2) clock
Figure 18-7. Examples Of Several TCLK Frequencies and Sample Rates
The PPM Module has two data transmit signals, PPM_TX[0:1], and two data receive
signals, PPM_RX[0:1]. The amount of data transferred on these signals depends on the
setting in PPMPCR[OP_16_8]. If the PPM is configured to transfer data in 16 PPM_TCLK
cycles per 16-bit word then all data, TX_DATA[0:15] is transmitted on the PPM_TX[0]
signal, and all data is received into RX_SHIFTER[0:15] from PPM_RX[0]. If the PPM is
configured to transfer data in eight PPM_TCLK cycles per 16-bit word then the eight bits
will transfer on each of the data transfer signals.
Care must be taken when setting the sample rate with respect
to the OP_16_8 bit setting. For example if the PPM is
transferring data on an 8-clock cycle, then setting the sample
rate to every 16 clocks will result in lost data.
18-8
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
NOTE
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