MPC8280 datasheet(778/1386 Pages) FREESCALE

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SCC Transparent Mode

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

24-4

Freescale Semiconductor

frame. Pulse operation allows an uninterrupted stream of data. However, use envelope mode to identify

frames of transparent data.

The sampling option determines the delay between CD and CTS being asserted and the resulting action by

the SCC. Assume either that these signals are asynchronous to the data and internally synchronized by the

SCC or that they are synchronous to the data with faster operation. This option allows RTS of one SCC to

be connected to CD of another SCC and to have the data synchronized and bit aligned. It is also an option

to link the transmitter synchronization to the receiver synchronization. Diagrams for the pulse/envelope

and sampling options are shown in Section 24.4, “Achieving Synchronization in Transparent Mode.”

24.4.1.2.1

External Synchronization Example

Figure 24-1 shows synchronization using external signals.

Figure 24-1. Sending Transparent Frames between MPC8280s

MPC8280 (A) and MPC8280 (B) exchange transparent frames and synchronize each other using RTS and

CD. However, CTS is not required because transmission begins at any time. Thus, RTS is connected

directly to the other MPC8280 CD pin. GSMR_H[RSYN] is not used and transmission and reception from

each MPC8280 are independent.

RXD

CLK

TXD

RTS

RXD

BRGO

RTS

TXD

CLK

BRGO

Last Bit of Frame Data

First Bit of Frame Data

(Output is CLK

x Input)

TXD

(Output is RXD Input)

RTS

(Output is CD Input)

or CRC

TxBD[L] = 1 Causes Negation of RTS

CD Lost Condition Terminates Reception of Frame

MPC8280 (A)

MPC8280 (B)

Notes:

1. Each MPC8280 generates its own transmit clocks. If the transmit and receive clocks are the same, one MPC8280

can generate transmit and receive clocks for the other MPC8280. For example, CLK

x on MPC8280 (B) could be used

to clock the transmitter and receiver.

2. CTS should be configured as always asserted in the parallel I/O or connected to ground externally.

3. The required GSMR configurations are DIAG= 00, CTSS=1, CTSP is a “don’t care”, CDS=1, CDP=0, TTX=1, and

TRX=1. REVD and TCRC are application-dependent.

4. The transparent frame contains a CRC if TxBD[TC] is set.

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