Input Capture - Rabbit 3000 User Manual

7.12 Input Capture

The two-channel Input Capture can be used to time input signals from various port pins.
Each Input Capture channel consists of a sixteen-bit counter that is clocked by the output
of Timer A8, and can be connected to one or two out of sixteen parallel port pins. The
Input Capture channel captures the state of its counter upon either of two programmed
conditions and can then generate an interrupt. The programmed conditions can also be
used to start and stop the counter.
Register Name
Input Capture Ctrl/Status Register
Input Capture Control Register
Input Capture Trigger 1 Register
Input Capture Source 1 Register
Input Capture LSB 1 Register
Input Capture MSB 1 Register
Input Capture Trigger 2 Register
Input Capture Source 2 Register
Input Capture LSB 2 Register
Input Capture MSB 2 Register
Because the Input Capture channels synchronize their inputs to the peripheral clock (fur-
ther divided by Timer A8), there is some delay between the input transition and when an
interrupt is requested, as shown below. The status bits in the ICSxR are set coincident with
the interrupt request and are reset when read from the ICSxR.
Peri Clock
Timer A8
CPT input
Interrupt
Each Input Capture channel has two inputs, called the Start condition and the Stop condi-
tion. Each of these two inputs can be programmed to come from one of four bits (bits 1, 3,
5 or 7) in Parallel Port C, D, F or G. The two inputs can come from the same or different
pins, and are edge-sensitive. Each input can be disabled, rising-edge-sensitive, falling-
edge-sensitive or responsive to either edge polarity. Either or both inputs can generate an
Input Capture interrupt, and either or both inputs can cause the current count to be latched.
User's Manual
Mnemonic I/O Address
ICCSR 0x56
ICCR 0x57
ICT1R 0x58
ICS1R 0x59
ICL1R 0x5A
ICM1R 0x5B
ICT2R 0x5C
ICS2R 0x5D
ICL2R 0x5E
ICM2R 0x5F
R/W Reset
R/W 00000000
W xxxxxx00
W 00000000
W xxxxxxxx
R xxxxxxxx
R xxxxxxxx
W 00000000
W xxxxxxxx
R xxxxxxxx
R xxxxxxxx
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