xr17v254 Exar Corporation, xr17v254 Datasheet - Page 18

• Manufacturer Part Number: xr17v254
• Description: 66mhz Pci Bus Quad Uart With Power Management Support
• Manufacturer: Exar Corporation

XR17V254
66MHZ PCI BUS QUAD UART WITH POWER MANAGEMENT SUPPORT
A 16-bit down-count timer for general purpose timer or counter. Its clock source may be selected from internal
crystal oscillator or externally on pin TMRCK. The timer can be set to be a single-shot for a one-time event or
re-triggerable for a periodic signal. An interrupt may be generated when the timer times out and will show up as
a Channel 0 interrupt (see
TIMELSB, TIMERMSB]. The TIMERCNTL register provides the Timer commands such as start/stop, as shown
in
diagram of the Timer/Counter circuit is shown below:
TIMERMSB [31:24] and TIMERLSB [23:16]
The concatentaion of the 8-bit registers TIMERMSB and TIMERLSB forms a 16-bit value which decides the
time-out period of the Timer, per the following equation:
The least-significant bit of the timer is being bit [0] of the TIMERLSB with most-significant-bit being bit [7] in
TIMERMSB. Notice that these registers do not hold the current counter value when read. Default value is zero
(timer disabled) upon powerup and reset. The ’Reset Timer’ command does not have any effect on this
register.
TIMER [15:8] Reserved
1.6.2
Table 10
Bit-15 Bit-14 Bit-13 Bit-12 Bit-11 Bit-10
F
IGURE
0
General Purpose 16-bit Timer/Counter [TIMERMSB, TIMELSB, TIMER, TIMECNTL] (
COM M ANDS
TIM ERCNTL
X
below. The time-out output of the Timer can also be optionally routed to the MPIO[0] pin. The block
TIM ERM SB and TIM ERLSB
XX-XX-00-00)
6. T
Timer output frequency = Timer input clock / 16-bit Timer value
OSC. CLOCK
IMER
TIMERMSB Register
(16-bit Value)
TM RCK
/C
Clock Select
Single shot/Re-triggerable
Start/Stop
Tim er Interrupt Enable/ Disable
Route/De-route to M PIO[0]
OUNTER CIRCUIT
Table 8
1
0
16-Bit Timer/Counter Programmable Registers
). It is controlled through 4 configuration registers [TIMERCNTL, TIMER,
.
Bit-9 Bit-8
Tim er/Counter
16-Bit
18
Bit-7
Tim er Interrupt
M PIOLVL[0]
Output
Tim er
Bit-6
1
0
Bit-5
TIMERLSB Register
Bit-4
M PIO[0]
1
0
Bit-3
Tim er Interrupt
No Interrupt
Bit-2
Bit-1 Bit-0
REV. 1.0.0
DEFAULT