snap ethernet-based i/o units protocols and programming guide

Read and clear latches for individual points.
CHAPTER 4: USING THE IEEE 1394-BASED PROTOCOL
To read latches for individual points, see the memory map area “Digital Point Read—Read
Only” on page 121, and use the on-latch or off-latch state starting address for the point you want
to read. For example, you would read off-latch status for point 0 starting at address
FFFFF0800002.
To read a bank of points, see the memory map area “Digital Bank Read—Read Only” on
page 119. The starting address for reading the state of on-latches is FFFFF0400008, and the
starting address for off-latches is FFFFF0400010.
To read and clear latches for individual points, see the memory map area “Digital Read and
Clear—Read Only” on page 132. If you are reading and clearing the on-latch at point 1, for
example, you would use the starting address FFFFF0F00104.
For help in understanding the data you read, see “Formatting and Interpreting Data” on page 41.
Counters
This feature applies to digital points on I/O units with the following brains only:
SNAP-UP1-ADS
SNAP-B3000-ENET
When configured, it will count the number of times the input changes from off to on. Using
counters involves two steps: configuring the counter and reading data.
Configuring a Counter
To configure a digital input as a counter, first configure the point as an input. Write to the
“Analog and Digital Point Configuration Information—Read/Write” area of the memory map.
(See page 125.) For example, to configure point 0 as a counter, you would write to the memory
map address FFFFF0C00004, using 00000100 as the data for a digital input.
Next, configure the point feature as a counter. In the same area of the memory map, for
point 0 you would write to the address FFFFF0C00008 and use 00000001 as the data for a counter.
Reading a Counter
SNAP-ENET-RTC
SNAP-WLAN-FH-ADS
You can:
Read counters for individual points and leave them counting
Read a bank of points and leave them counting
Read and clear individual point counters in one step, setting the counters back to zero.
To read counters for individual points, see the memory map area “Digital Point Read—Read
Only” on page 121, and use the counter data starting address for the point you want to read. For
example, you would read counter data for point 1 starting at address FFFFF0800044.
SNAP Ethernet-Based I/O Units Protocols and Programming Guide 89