Motorola MPC8260 - Manual (Page 777)

MOTOROLA Chapter 28. Fast Communications Controllers (FCCs) 28-19
Part IV. Communications Processor Module
Figure 28-9. Using CD to Control Reception
If it is programmed to envelope data, CD must remain asserted during frame transmission
or a CD lost error occurs. The negation of CD terminates reception. If [CDS] = 0, CD must
be sampled by the FCC before a CD lost is recognized. Otherwise, the negation of CD
immediately causes the CD lost condition.
Note that if GFMR[CDS] = 1, all CD transitions must occur while the receive clock is low.
28.12 Disabling the FCCs On-the-Fly
Unused FCCs can be temporarily disabled. In this case, a operation sequence is followed
that ensures that any buffers in use are closed properly and that new data is transferred to
or from a new buffer. Such a sequence is required if the parameters that must be changed
are not allowed to be changed dynamically. If the register or bit description states that
dynamic changes are allowed, the following sequences are not required and the register or
bit may be changed immediately. In all other cases, the sequence should be used.
Modifying parameter RAM does not require the FCC to be fully disabled. See the
parameter RAM description for when values can be changed. To disable all peripheral
controllers, set CPCR[RST] to reset the entire CPM.
1. GFMR_H[CDS] = 0. CDP=0.
RCLK
First Bit of Frame Data
Notes:
CD Sampled Low
RCLK
CD Sampled High
Last Bit of Frame Data
2. If CD is negated prior to the last bit of the receive frame, CD lost is signaled in the BD.
3. If CDP=1, CD lost cannot occur and CD negation has no effect on reception.
1. GFMR_H[CDS] = 1. CDP=0.
Notes:
2. If CD is negated prior to the last bit of the receive frame, CD lost is signaled in the BD.
3. If CDP=1, CD lost cannot occur and CD negation has no effect on reception.
Last Bit of Frame Data First Bit of Frame Data
CD Assertion Immediately
Gates Reception CD Negation Immediately
Halts Reception
RXD
(Input)
CD
(Input)
CD
(Input)
RXD
(Input)