MC68340 datasheet(310/441 Pages) FREESCALE

310 / 441 page

MOTOROLA

MC68340 USER’S MANUAL

7- 15

(a) Automatic Echo

(b) Local Loopback

DISABLED

TxDx

OUTPUT

RxDx

INPUT

RxDx

INPUT

RxDx

INPUT

TxDx

OUTPUT

TxDx

OUTPUT

DISABLED

CPU

DISABLED

Figure 7-7. Looping Modes Functional Diagram

7.3.4 Multidrop Mode

A channel can be programmed to operate in a wakeup mode for multidrop or

multiprocessor applications. Functional timing information for the multidrop mode is shown

in Figure 7-8. The mode is selected by setting bits 3 and 4 in mode register 1 (MR1). This

mode of operation allows the master station to be connected to several slave stations

(maximum of 256). In this mode, the master transmits an address character followed by a

block of data characters targeted for one of the slave stations. The slave stations have

their channel receivers disabled. However, they continuously monitor the data stream sent

out by the master station. When an address character is sent by the master, the slave

receiver channel notifies its respective CPU by setting the RxRDY bit in the SR and

generating an interrupt (if programmed to do so). Each slave station CPU then compares

the received address to its station address and enables its receiver if it wishes to receive

the subsequent data characters or block of data from the master station. Slave stations

not addressed continue to monitor the data stream for the next address character. Data

fields in the data stream are separated by an address character. After a slave receives a

block of data, the slave station's CPU disables the receiver and initiates the process

again.

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