xr88c681 Exar Corporation, xr88c681 Datasheet - Page 54

• Manufacturer Part Number: xr88c681
• Description: Cmos Dual Channel Uart Duart
• Manufacturer: Exar Corporation

D.3 Counter/Timer
The Timing Control Block also contains a 16 bit
Counter/Timer (C/T). The C/T is a programmable 16 bit
down-counter which can use one of several timing
sources as its input. Figure 28 presents a block diagram
of the circuitry surrounding the C/T. The selection of these
Bit 6
Rev. 2.11
0
0
0
0
1
1
1
1
Bit 5
0
0
1
1
0
0
1
1
Oscillator
Circuit
TXCB
TXCA
IP2
Figure 28. A Block Diagram of the Circuitry Associated with the
Bit 4
0
1
0
1
0
1
0
1
Divide by 16
Divide by 16
Table 16. ACR[6:4] Bit Field Definition - C/T
C/T Mode
Counter
Counter
Counter
Counter
Timer
Timer
Timer
Timer
Counter/Timer
Preset Registers
(CTUR, CTLR)
Counter/Timer
54
ACR[4-6]
timing sources for the Counter/Timer can be made by
writing the appropriate data to ACR[6:4] (Auxiliary Control
Register bits 6 through 4). Please see Table 16 for the
relationship between the Counter/Timer mode, the
Timing Source and ACR[6:4]. The C/T output is available
to the Clock Select Registers for use as a programmable
bit rate generator for both Transmitters and Receivers.
Timing Source
External Input - IP2
TXCA 1X - Clock of Channel A Transmitter
TXCB 1X - Clock of Channel B Transmitter
X1/CLK Input Divided by 16
External Input - IP2
External Input - IP2, Divided by 16
X1/CLK Input
X1/CLK Input Divided by 16
C/T_RDY
to 32:1 MUXs
(OP3)