XR88C681CP/40 Exar Corporation, XR88C681CP/40 Datasheet - Page 86

• Manufacturer Part Number: XR88C681CP/40
• Description: Dual Channel UART
• Manufacturer: Exar Corporation

Specifications of XR88C681CP/40

• Features: *
• Number Of Channels: 2, DUART
• Fifo's: 1 Byte, 3 Byte
• Voltage - Supply: 5V
• With Parallel Port: Yes
• With Cmos: Yes
• Mounting Type: Through Hole
• Package / Case: 40-DIP (0.600", 15.24mm)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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,
Rev. 2.11
Figure 48. A Flow Diargam Depicting a Procedure That Can Be Used to
Character to Slave Device.
(Write Character to THRn)
Invoke the “RESET MR
POINTER” command.
(Write 1xh to appropriate
Command Register)
Invoke the “RESET MR
POINTER” command.
(Write 1xh to appropriate
Command Register)
Transmit Address
(Write xxxxx1xx to
Transmit Characters in the Multi-Drop Mode
MR1n Register)
Set A/D Bit to “1”
START
86
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.
Transmit Data Character
(Write Character to THRn)
(Write xxxxx0xx to MR1n
to Write to Active
Data Characters
Set A/D Bit to “0”
Are there More
to Slave Device.
Slave Device?
Register)
No
Yes