XR88C681J-F Datasheet, PDF (86/101 Pages) Exar Corporation – Two Full Duplex, Independent Channels

XR88C681
An Address Byte, however, interrupts all “Slaves” so that
each can examine the received byte to test if it (the
individual slave device) is being addressed. The receiver
of the addressed slave will be enabled and will prepare for
reception of the data bytes that follows. The slaves that
were not addressed will leaves their Receivers disabled,
and will continue to ignore the data bytes that follows.
They will be interrupted again when the next address byte
is transmitted by the “Master Device”.
H.2.2 DUART Multi-Drop Operation
A given channel, within the DUART is programmed into
the Multi-Drop mode by setting MR1n[4:3] = “1, 1”. In this
mode, a transmitted character consists of a START bit,
the programmed number of data bits, the Address/Data
(A/D) flag bit; and the programmed STOP bit length. A/D
= 0 indicates that the character is data, while A/D = 1
identifies it as an address.
Transmitter Operation During Multi-Drop Mode
The user/CPU controls the state of the transmitted
character by programming MR1n[2] of the channel prior
to loading the data bits into the THR. Setting MR1n[2] =
“0” results in A/D = “0” and setting MR1n[2] = “1” results in
A/D = “1”. Figure 48 presents a procedural flow diagram
for transmitting characters (Address or Data), while in the
Multi-Drop Mode.
START
Invoke the “RESET MR
POINTER” command.
C(Wormitem1axnhd ^{tRoeagpisptreorp)riate}
(WritSeextxAx/xDx0Bxixt ^{ttoo“M0”R1n}
Register)
Set A/D Bit to “1”
(Write xxxxx1xx to
MR1n Register)
Transmit Address
Character to Slave Device.
(Write Character to THRn)
Invoke the “RESET MR
POINTER” command.
(Write 1xh to appropriate
Command Register)
Transmit Data Character
to Slave Device.
(Write Character to THRn)
Are there More
Data Characters
Yes
to Write to Active
Slave Device?
No
Rev. 2.11
Figure 48. A Flow Diargam Depicting a Procedure That Can Be Used to
Transmit Characters in the Multi-Drop Mode
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