MPC8280 datasheet(590/1386 Pages) FREESCALE

590 / 1386 page

Serial Interface with Time-Slot Assigner

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

15-12

Freescale Semiconductor

Figure 15-8 shows how SWTR can be used.

Figure 15-8. Using the SWTR Feature

The SWTR option lets station B listen to transmissions from station A and send data to station A. To do

this, station B would set SWTR in its receive route RAM. For this entry, receive data is taken from the

L1TXD pin and data is sent on the L1RXD pin. If the user wants to listen only to station A transmissions

and not send data on L1RXD, the CSEL bits in the corresponding transmit route RAM entry should be

cleared to prevent transmission on the L1RXD pin.

Station B can transmit data to station A by setting the SWTR bit of the entry in its receive route RAM.

Data is sent on L1RXD rather than L1TXD, according to the transmit route RAM. Note that this

configuration could cause collisions with other data on L1RXD unless an available (quiet) time slot is

used. To transmit on L1RXD and not receive data on L1TXD, clear the CSEL bits in the receive route

RAM.

NOTE

If the transmit and receive sections of the TDM do not use a common clock

source, the SWTR feature can cause erratic behavior. Also note, this feature

does not work with nibble operation.

When MCC = 1, the SIx RAM entry fields function as described in Table 15-2.

BYT

Byte resolution

0 Bit resolution. The CNT value indicates the number of bits in this group.

1 Byte resolution. The CNT value indicates the number of bytes in this group.

LST

Last entry in the RAM. Whenever SI

x RAM is used, LST must be set in one of the Tx or Rx entries

of each group. Even if all entries of a group are used, this bit must still be set in the last entry.

0 Not the last entry in this section of the route RAM.

1 Last entry in this RAM. After this entry, the SI waits for the sync signal to start the next frame.

Note: There must be only an even number of entries in an SI

x RAM frame, because LST is active

only in odd-numbered entries (assuming the entry count starts with 0). Therefore, to obtain

an even number of entries, an entry may need to be split into two entries.

Also note that, to avoid errors in switching to and from shadow SI RAM, the last entry in SI RAM

should not be programmed to 1-bit resolution (i.e. CNT = 000 and BYT = 0).

Table 15-1. SI

x RAM Entry (MCC = 0) (continued)

Bits

Name

Description

Station A

Station B

L1TXD

L1RXD

Station A

Station B

L1TXD

L1RXD

Tx and Rx SI

x RAMn[SWTR] = 1

Tx and Rx SI

x RAMn[SWTR] = 0

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