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XR88C681J-F Datasheet, PDF (18/101 Pages) Exar Corporation – Two Full Duplex, Independent Channels | |||
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XR88C681
Bit 7
1
1
1
1
Bit 6
1
1
1
1
Bit 5
0
0
1
1
Bit 4
0
1
0
1
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 âSET
ACTIVE MODEâ 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
âhighâ.
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 DUARTâs operation while
in the Z-Mode, Please see Section C.6.2. (Not avail-
able for the 28 pin DIP packaged devices)
Reserved.
Reserved.
Table 3. Miscellaneous Commands, Upper Nibble of all Command Registers,
Unless Otherwise Specified (Contâd)
In addition to the commands which are available through
the command registers, the DUART also offers
âAddress-Triggeredâ commands. These commands are
listed in Table 1, âDUART PORT AND REGISTER
ADDRESSINGâ; and are further identified by being
âshadedâ 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 0E16. Please
note that this âRead Operationâ will not result in placing
the contents of a DUART register on the data bus. The
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 âSET OUTPUT PORT BITSâ Command. This
command is invoked by performing a write of data to
DUART address 0E16. When the user invokes this
command, he/she is setting certain bits (to â1â) 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 â1â, the state of
the corresponding output port pin, OP0, is now set to a
logic â0â. Consequently, one can think of the âSET
OUTPUT PORT BITSâ command as the âCLEAR
OUTPUT PORT PINSâ command. For a more detailed
discussion into the operation of the Output Ports, please
see Section F.
Rev. 2.11
18
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