User`s manual
PK2100
I/O Configurations s 3-7
Three of the digital inputs also serve as counter inputs. In addition, there
is a special differential counter input. The counter inputs are arranged as
shown in Figure 3-7.
+
U34, RS-485 receive
C1A
C1B
C2A
C2B+
C2B
C2B
/DREQ0
/DREQ1
CKA1
Counter 1
Counter 2
J8:7-8
J8:9-10
+5 V
+5 V
+5 V
r
Figure 3-7. Digital Inputs Used As Counter Inputs
The counters count on a negative-going edge. Each counter has two
inputs, which are symmetrical in that one can be used as a gate and the
other can be used as a count input.
The RS-485 receiver input can be used as a digital input by attaching one
side of it to the desired threshold voltage. This input can be used as a true
differential input for such devices as inductive pickups. It has a common-
mode voltage range from -12 to +12 volts with an input hysteresis of
50millivolts.
An internal jumper can connect the signal from input/output procesor
CKA1, which is controlled by the second (RS-485) serial ports hardware.
CKA1 can be set to count pulses at 100 kHz or more down to a few
hundred hertz.
The counters are implemented by using the DMA channels of the Z180
microprocessor. The maximum count speed is more than 100 kHz. The
DMA channel can be programmed to store a byte from an input/output
port to memory for each count, if desired. This byte can be the least
significant byte of the internal programmable counter (PRT), which
allows the count edge to be localized in time. This feature can also
determine the