XR88C681J-F Datasheet, PDF (85/101 Pages) Exar Corporation – Two Full Duplex, Independent Channels

Master Device
TXDn
XR88C681
RXDn
00h
RXDn
01h
RXDn
02h
Slave Devices
RXDn
FFh
Figure 46. An Illustration Depicting the Concept of Multi-Drop Mode
LSB
8 Bit Character
MSB A/D
Address/Data Bit
Figure 47. Bit Format of Character Data Being Transmitted in the Multi-Drop Mode
The “Master Station” communicates to the “Slave
Stations” by transmitting a character (typically a byte) with
an “Address/Data” bit flag appended to the end of the
character. This typically results in nine bits of being
transmitted for every character byte, as presented in
Figure 47.
When the “Master Station” wants to transmit a block of
data to one of several slaves, it first sends out an Address
byte that identifies the “Target Slave”. An address byte
differs from a data byte in that the ninth bit is a “1” in an
Address Byte and a “0” in a Data Byte.
Rev. 2.11
85