Special Registers
EBX-37 Reference Manual
63
The 32-bit cascade mode is set in TM4MODE in the Timer Control Register. There are also
internal or external clock selections for the timers in this register using the external clocks ICTC3
and ICTC4 signals on the connector at J22. The internal clock is the PCI clock divided by 8
(33.33 MHz / 8 = 4.167 MHz). ICTC3 can only be used with Timer 3. ICTC4 can only be used
with Timer 4. The clock for Timer 5 is always the internal clock except in the 32-bit cascade
mode when the output from Timer 4 is the clock for Timer 5.
The timer outputs can generate interrupts. When a timer output transitions from a 0 to a 1 then an
interrupt status bit is set and can generate an interrupt. This bit sticks until cleared.
