XR88C681CP/40 Exar Corporation, XR88C681CP/40 Datasheet - Page 18

• 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

In addition to the commands which are available through
the command registers, the DUART also offers
“Address-Triggered” commands. These commands are
listed in Table 1, “DUART PORT AND REGISTER
ADDRESSING”;
“shaded” in Table 1. Specifically, these commands are:
D START COUNTER/TIMER COMMAND
D STOP COUNTER/TIMER COMMAND
D SET OUTPUT PORT BITS COMMAND
D CLEAR OUTPUT PORT BITS COMMAND
Each of these commands are invoked by either reading or
writing data to their corresponding DUART addresses as
specified in Table 1.
For Example:
The START COUNTER/TIMER COMMAND is invoked by
the procedure of reading DUART address 0E
note that this “Read Operation” will not result in placing
the contents of a DUART register on the data bus. The
Rev. 2.11
Bit 7
1
1
1
1
Table 3. Miscellaneous Commands, Upper Nibble of all Command Registers,
and are further identified by being
Bit 6
1
1
1
1
Unless Otherwise Specified (Cont’d)
Bit 5
0
0
1
1
16
. Please
Bit 4
18
0
1
0
1
only thing that will happen, in response to this procedure
is the Counter/Timer will initiate counting. For a detailed
discussion into the operation of the Counter/Timer, please
see Section D.2.
Another example of an Address-Triggered commands is
the “SET OUTPUT PORT BITS” Command.
command is invoked by performing a write of data to
DUART address 0E
command, he/she is setting certain bits (to “1”) within the
OPR (Output Port Register). All other bits, within the OPR
(not specified to be set), are not changed. The state of the
output port pins are complements of the individual bits
within the OPR. Hence, if OPR[0] is set to “1”, the state of
the corresponding output port pin, OP0, is now set to a
logic “0”.
OUTPUT PORT BITS” command as the “CLEAR
OUTPUT PORT PINS” command. For a more detailed
discussion into the operation of the Output Ports, please
see Section F.
Description
Set Standby Mode (Channel A). When this com-
mand is invoked via the Channel A Command Regis-
ter, power is removed from each of the transmitters,
receivers, counter/timer and additional circuits to
place the DUART in the standby (or lower power)
mode. Please note that this command effects the
operation of the entire chip. Normal operation is re-
stored by a hardware reset or by invoking the “SET
ACTIVE MODE” command.
Reset IUS Latch (Channel B). When this command
is invoked via the Channel B Command Register,
and the DUART is operating in Z-mode, it causes
the Interrupt-Under-Service (IUS) latch to be reset.
This, in turn, will cause the IEO output to toggle
“high”.
Set Active Mode (Channel A). When this com-
mand is invoked via the Channel A Command Regis-
ter, the DUART is removed from the Standby Mode
and resumes normal operation.
Set Z-Mode (Channel B). When this command is
invoked via the Channel B Command Register, the
DUART is conditioned to operate in the Z-Mode. For
a detailed discussion of the DUART’s operation while
in the Z-Mode, Please see Section C.6.2. (Not avail-
able for the 28 pin DIP packaged devices)
Reserved.
Reserved.
Consequently, one can think of the “SET
16
.
When the user invokes this
This