at94k10al ATMEL Corporation, at94k10al Datasheet - Page 89

• Manufacturer Part Number: at94k10al
• Description: At94k05al 5k - 40k Gates Of At40k Fpga With 8-bit Microcontroller, Up To 36k Bytes Of Sram And On-chip Jtag Ice
• Manufacturer: ATMEL Corporation

4.23
4.24
1138I–FPSLI–1/08
Timer/Counters
Timer/Counter Prescalers
The FPSLIC provides three general-purpose Timer/Counters: two 8-bit T/Cs and one 16-bit T/C.
Timer/Counter2 can optionally be asynchronously clocked from an external oscillator. This oscil-
lator is optimized for use with a 32.768 kHz watch crystal, enabling use of Timer/Counter2 as a
Real-time Clock (RTC). Timer/Counters 0 and 1 have individual prescaling selection from the
same 10-bit prescaling timer. Timer/Counter2 has its own prescaler. Both these prescalers can
be reset by setting the corresponding control bits in the Special Functions I/O Register (SFIOR).
See “Special Function I/O Register – SFIOR” on page 90 for a detailed description. These
Timer/Counters can either be used as a timer with an internal clock time-base or as a counter
with an external pin connection which triggers the counting.
For Timer/Counters 0 and 1, see
CK/256 and CK/1024, where CK is the oscillator clock. For the two Timer/Counters 0 and 1, CK,
external source, and stop, can also be selected as clock sources. Setting the PSR10 bit in
SFIOR resets the prescaler. This allows the user to operate with a predictable prescaler. Note
that Timer/Counter1 and Timer/Counter0 share the same prescaler and a prescaler reset will
affect both Timer/Counters.
Figure 4-25. Prescaler for Timer/Counter0 and 1
The clock source for Timer/Counter2 prescaler, see
default connected to the main system clock CK. By setting the AS2 bit in ASSR, Timer/Counter2
is asynchronously clocked from the TOSC1 pin. This enables use of Timer/Counter2 as a Real-
time Clock (RTC). When AS2 is set, pins TOSC1 and TOSC2 are disconnected from Port D. A
crystal can then be connected between the TOSC1 and TOSC2 pins to serve as an independent
clock source for Timer/Counter2. The oscillator is optimized for use with a 32.768 kHz crystal.
Alternatively, an external clock signal can be applied to TOSC1. The frequency of this clock
must be lower than one fourth of the CPU clock and not higher than 1 MHz. Setting the PSR2 bit
in SFIOR resets the prescaler. This allows the user to operate with a predictable prescaler.
PSR10
Figure
TCK1
Clear
4-25, the four prescaled selections are: CK/8, CK/64,
AT94KAL Series FPSLIC
Figure
4-26, is named PCK2. PCK2 is by
TCK0
89