MOTOROLA
Chapter 21. Serial Interface
21-15
Part V. The Communications Processor Module
For applications needing to receive data from a Tx signal and send data on an Rx signal, set
SIRAMn[SWTR]. For example, stations A and B in Figure 21-11 use different time slots
on one TDM channel. Even though they share Rx and Tx data lines, stations A and B can
communicate using the SWTR option.
Figure 21-11. Example Using SI RAMn[SWTR]
The SWTR option allows station B to listen to transmissions from and send data to station
A. By setting SWTR in its Rx route RAM entry, station B receives data from L1TXD and,
if the time slotÕs Tx route RAM entry allows, sends data on L1RXD. To prevent sending on
L1RXD while listening to station A, clear the CSEL bits in the corresponding Tx route
RAM entries. Conversely, to prevent receiving on L1TXD while sending on L1RXD, clear
the CSEL bits in corresponding Rx SI RAM entries. Note that using the SWTR option may
cause data collisions with other stations unless an empty (quiet) time slot is used.
21.2.3.8 SI RAM Programming Example
This section shows how to program the SI RAM to support the 10-bit IDL bus whose format
is shown in Figure 21-26. Here, the TSA supports the B1 channel with SCC2, the D channel
with SCC3, the Þrst 4 bits of the B2 channel with an external device (using a strobe to
enable the external device), and the last 4 bits of B2 with SMC1. Additionally, the TSA
marks the D channel with another strobe signal.
10Ð13 CNT
Count. The number of bits/bytes (the unit is determined by BYT) that the routing and strobe select of
this entry controls. If CNT = 0b0000, 1 bit/byte is routed; if CNT = 0b1111, 16 bits/bytes are routed.
14
BYT
Byte resolution.
0 Bit resolution. CNT indicates the number of bits in this entry.
1 Byte resolution. CNT indicates the number of bytes in this entry.
15
LST
Last entry in a TDM channelÕs Rx or Tx SI RAM. LST must be set in the last entry even if all the
entries are used.
0 Not the last entry in this TDM channelÕs Rx or Tx SI RAM.
1 Last entry. After this entry, the SI waits for SYNC to start the next frame.
16Ð31 Ñ
Reserved
Table 21-2. SIRAM Field Descriptions (Continued)
Bits
Name
Description
Rx
Station A
Tx
Rx
Station B
Tx
L1TXD
L1RXD
Rx
Station A
Tx
Tx
Station B
Rx
L1TXD
L1RXD
Tx and Rx SI RAM
n
[SWTR] = 1
Tx and Rx SI RAM
n
[SWTR] = 0
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