Motorola MPC8260 - Manual (Page 657)

MOTOROLA Chapter 23. SCC Transparent Mode 23-5
Part IV. Communications Processor Module
Figure 23-1. Sending Transparent Frames between MPC8260s
MPC8260(A) and MPC8260(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 MPC8260 CD pin. GSMR_H[RSYN] is not
used and transmission and reception from each MPC8260 are independent.
23.4.1.3 Transparent Mode without Explicit Synchronization
If there is no need to synchronize the transparent controller at a speciÞc point, the user can
ÔfakeÕ synchronization in one of the following ways:
¥ Tie a parallel I/O pin to the CTS and CD lines. Then, after enabling the receiver and
transmitter, provide a falling edge by manipulating the I/O pin in software.
¥ Enable the receiver and transmitter for the SCC in loopback mode and then change
GSMR_L[DIAG] to 0b00 while the transmitter and receiver and enabled.
23.4.2 Synchronization and the TSA
A transparent-mode SCC using the time-slot assigner can synchronize either on a user-
deÞned inline pattern or by inherent synchronization.
RXD
CD
CLKx
TXD
RTS CD
RXD
BRGOx
RTS
TXD
CLKx BRGOx
BRGOx
Last Bit of Frame Data
First Bit of Frame Data
(Output is CLKx 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
MPC8260 (A) MPC8260 (B)
Notes:
1. Each MPC8260 generates its own transmit clocks. If the transmit and receive clocks are the same, one MPC8260
can generate transmit and receive clocks for the other MPC8260. For example, CLKx on MPC8260 (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 conÞgurations are DIAG= 00, CTSS=1, CTSP is a ÒdonÕt careÓ, 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.