XR88C681CP/40 Exar Corporation, XR88C681CP/40 Datasheet - Page 15

• 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

Note: The shaded blocks are not Read/Write registers but are rather “Address-Triggered” Commands.
Table 1 indicates that each channel is equipped with two Mode Registers. Associated with each of these Mode Register
pairs is a “Mode Register” pointer or MR pointer. Upon chip/system power up or RESET each MR pointer is “pointing to”
the channel MR1n register. (Please note that the suffix “n” is used at the end of many of the DUART registers symbols in
order to refer, generically, to either channels A or B). However, the contents of the MR pointer will shift from the address
of the MR1n register to that of the MR2n register, immediately following any Read or Write access to the MR1n register.
The MR pointer will continue to “point to” the MR2n register until a hardware reset occurs or until a “RESET MR
POINTER” command has been invoked. The “RESET MR POINTER” command can be issued by writing the
Address (Hex)
Rev. 2.11
0A
0B
0C
0D
0E
00
01
02
03
04
05
06
07
08
09
0F
Counter/Timer Upper
Counter/Timer Lower
Rx Holding Register,
Rx Holding Register,
Start Counter/Timer
Stop Counter/Timer
Input Port Change
Masked Interrupt
Status Register,
Status Register,
Interrupt Status
Interrupt Vector
Register Name
Mode Register,
Status Register
Mode Register,
Byte Register
Byte Register
RESERVED
Channel A
Channel A
Channel A
Channel B
Channel B
Channel B
Command
Command
Input Port
Register
Register
Register
Table 1. DUART Port and Register Addressing
Read Mode Registers
MR1A, MR2A
MR1B, MR2B
Symbol
RHRA
RHRB
MISR
IPCR
SRA
CTU
SRB
SCC
STC
CTL
ISR
IVR
15
IP
Interrupt Mask Register
Configuration Register
Clock Select Register,
Clock Select Register,
Clear Output Port Bits
Counter/Timer Lower
Command Register A
Tx Holding Register,
Upper Byte Register
Tx Holding Register,
Command Register,
Set Output Port Bits
Auxiliary Control
Interrupt Vector
Register Name
Mode Register,
Mode Register,
Counter/Timer
Byte Register
(OP0 - OP7)
Output Port
Channel A
Channel A
Channel A
Channel B
Channel B
Channel B
Channel B
Command
Command
Register
Register
Write Mode Registers
XR88C681
MR1A, MR2A
MR1B, MR2B
Symbol
SOPBC
COPBC
OPCR
CSRA
THRA
CSRB
THRB
CRA
ACR
CTU
CRB
CTL
IMR
IVR