XR17V252 Datasheet, PDF (17/69 Pages) Exar Corporation – 66 MHZ PCI BUS DUAL UART WITH POWER MANAGEMENT SUPPORT

REV. 1.0.1
XR17V252
66 MHZ PCI BUS DUAL UART WITH POWER MANAGEMENT SUPPORT
1.6.2
General Purpose 16-bit Timer/Counter [TIMERMSB, TIMELSB, TIMER, TIMECNTL] (DEFAULT
0XXX-XX-00-00)
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 Table 8). It is controlled through 4 configuration registers [TIMERCNTL, TIMER,
TIMELSB, TIMERMSB]. The TIMERCNTL register provides the Timer commands such as start/stop, as shown
in Table 10 below. The time-out output of the Timer can also be optionally routed to the MPIO[0] pin. The block
diagram of the Timer/Counter circuit is shown below:
FIGURE 6. TIMER/COUNTER CIRCUIT.
TIMERMSB and TIMERLSB
(16-bit Value)
TMRCK
1
OSC. CLOCK
0
16-Bit
T im er/C ounter
T im er
Output
1
0
Clock Select
Start/Stop
TIMERCNTL
COM M ANDS ^{Single shot/Re-triggerable}
Timer Interrupt Enable/ Disable
M P IO L VL [0 ]
Timer Interrupt
Route/De-route to MPIO[0]
M PIO [0]
1
Timer Interrupt
0
No Interrupt
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:
Timer output frequency = Timer input clock / 16-bit Timer value
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.
16-Bit Timer/Counter Programmable Registers
TIMERMSB Register
TIMERLSB Register
Bit-15 Bit-14 Bit-13 Bit-12 Bit-11 Bit-10 Bit-9 Bit-8
Bit-7 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2 Bit-1 Bit-0
TIMER [15:8] Reserved
17