HD64570 Datasheet, PDF (32/469 Pages) Hitachi Semiconductor – Serial Communications Adaptor

1.7 General Description of Functions
1.7.1 Operating Modes of Serial Section
The normal SCA operating mode is full duplex (figure 1.6). The SCA can transmit and receive
simultaneously, using two separate lines.
In auto echo mode (figure 1.6), the SCA automatically retransmits all received data. Data received
on the RXD line are retransmitted on the TXD line, and received data are simultaneously input to
the receiver in the SCA.
In local loop back mode (figure 1.6), transmit data supplied to the SCA are automatically
transferred to the receive data buffer in the SCA. Data received on the RXD line are retransmitted
on the TXD line.
A
B
Full duplex
(simultaneous transmit and receive)
SCA
TxD
RxD
Auto echo mode
TxD
SCA
RxD
Local loop back mode
Figure 1.6 Operating Modes
1.7.2 Transmission Formats
The SCA supports asynchronous, byte-synchronous (bisync, X.21, DDCMP, etc.) and bit-
synchronous (frame relay, HDLC, SDLC, X.25 link level/LAPB, LAPD, etc.) protocols. Each
communication mode has its own format for transmitting data (figure 1.7).
Rev. 0, 07/98, page 16 of 453