Jameco Electronics 3000 User Manual

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.

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.

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.

Input Capture Ctrl/Status Register

ICCSR

0x56

R/W

00000000

Input Capture Control Register

ICCR

0x57

W

xxxxxx00

Input Capture Trigger 1 Register

ICT1R

0x58

W

00000000

Input Capture Source 1 Register

ICS1R

0x59

W

xxxxxxxx

Input Capture LSB 1 Register

ICL1R

0x5A

R

xxxxxxxx

Input Capture MSB 1 Register

ICM1R

0x5B

R

xxxxxxxx

Input Capture Trigger 2 Register

ICT2R

0x5C

W

00000000

Input Capture Source 2 Register

ICS2R

0x5D

W

xxxxxxxx

Input Capture LSB 2 Register

ICL2R

0x5E

R

xxxxxxxx

Input Capture MSB 2 Register

ICM2R

0x5F

R

xxxxxxxx