MPC8280 datasheet(958/1386 Pages) FREESCALE

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Fast Communications Controllers (FCCs)

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

30-20

Freescale Semiconductor

Figure 30-12. 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

If GFMR[CDS] = 1, all CD transitions must occur while the receive clock

is low.

30.12 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[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[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)

RXD

(Input)

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