Rockwell Automation 1771-IS 5V DC INPUT MOD - Manual (Page 20)

Chapter
3
3-1
Programming and Operation
Switch status data is stored in the module, transferred to the data table
upon request by block transfer instructions, then stored in a data table file
until operated upon by user program instructions.
The user-selectable scan rates are 15.3 msec (normal) and 5.1 msec (fast).
The nine enable lines, A through I, are sequentially and repeatedly
enabled, one line at a time. The enable lines operate in a low = TRUE
logic. Each enable line can enable a bank of 8 switches simultaneously.
The module allows for contact debouncing before the module’s
microprocessor reads the status of the switch bank. Scanning is
continuous unless interrupted by a user program instruction to transfer the
status of the switch contacts to the data table. Scanning resumes at the
same point where it was interrupted after the data is transferred.
BCD thumbwheel switches convert selected decimal numbers to a switch
status setting. Four switch contacts are required to encode each decimal
digit of a thumbwheel switch in BCD. Switch status can be transferred to
the processor data table and stored in word format by user program
instructions (Figure 3.1).
Figure 3.1
Bit Pattern of a Thumbwheel Setting
Thumbwheel settings
Digit place labels
0 0 1 0 1 0 0 1
2 9 5 1
10369
0 1 0 1 0 0 0 1
MSD UMD LMD LSD
Switch status setting
Switch terminal numbers
Bit numbers
Equivalent bit pattern
(1 data table word)
8 4 2 1 8 4 2 1 8 4 2 1 8 4 2 1
17 10 07 00
General
Module Scan of Switch Contacts
Storage of Switch Contact Data