LM3S5K36 Datasheet, PDF (460/1050 Pages) Texas Instruments – Stellaris® LM3S5K36 Microcontroller

General-Purpose Timers
Table 10-5. 16-Bit Timer With Prescaler Configurations (continued)
Prescale (8-bit value)
# of Timer Clocks (Tc)^a
Max Time
00000010
3
2.4576
------------
--
--
11111101
254
208.0768
11111110
255
208.896
11111111
256
209.7152
a. Tc is the clock period.
Units
ms
--
ms
ms
ms
Wait-for-Trigger Mode
The Wait-for-Trigger mode allows daisy chaining of the timer modules such that once configured,
a single timer can initiate mulitple timing events using the Timer triggers. Wait-for-Trigger mode is
enabled by setting the TnWOT bit in the GPTMTnMR register. When the TnWOT bit is set, Timer N+1
does not begin counting until the timer in the previous position in the daisy chain (Timer N) reaches
its time-out event. The daisy chain is configured such that GPTM1 always follows GPTM0 and
GPTM2 follows GPTM1. If Timer A is in 32-bit mode (controlled by the GPTMCFG bit in the GPTMCFG
register), it triggers Timer A in the next module. If Timer A is in 16-bit mode, it triggers Timer B in
the same module, and Timer B triggers Timer A in the next module. Care must be taken that the
TAWOT bit is never set in GPTM0. Figure 10-2 on page 460 shows how the GPTMCFG bit affects the
daisy chain. This function is valid for both one-shot and periodic modes.
Figure 10-2. Timer Daisy Chain
GP Timer N+1
10
GPTMCFG
Timer B
Timer A
Timer B ADC Trigger
Timer A ADC Trigger
GP Timer N
10
GPTMCFG
Timer B
Timer A
Timer B ADC Trigger
Timer A ADC Trigger
10.3.2.2
Real-Time Clock Timer Mode
In Real-Time Clock (RTC) mode, the concatenated versions of the Timer A and Timer B registers
are configured as an up-counter. When RTC mode is selected for the first time after reset, the
counter is loaded with a value of 0x1. All subsequent load values must be written to the GPTM
Timer A Interval Load (GPTMTAILR) register (see page 488). Table 10-6 on page 460 shows the
values that are loaded into the timer registers when the timer is enabled.
Table 10-6. Counter Values When the Timer is Enabled in RTC Mode
Register
TnR
TnV
Count Down Mode
Not available
Not available
Count Up Mode
0x1
0x1
460
January 21, 2012
Texas Instruments-Production Data