Allen-Bradley MicroLogix 1200 Reference Manual page 93

Overflow (OVF)
Description Address
OVF - Overflow HSC:0.OVF
The OVF (Overflow) defines the upper count limit for the counter. If the
counter's accumulated value increments past the value specified in this
variable, an overflow interrupt is generated. When the overflow interrupt
is generated, the HSC sub-system rolls the accumulator over to the
underflow value and the counter continues counting from the underflow
value (counts are not lost in this transition). The user can specify any
value for the overflow position, provided it is greater than the underflow
value and falls between -2,147,483,648 and 2,147,483,647.
To load data into the overflow variable, the control program must toggle
(low to high) the Set Parameters (HSC:0.0/SP) control bit. When the SP bit
is toggled high, the data currently stored in the HSC function file is
transferred/loaded into the HSC sub-system.
Data loaded into the overflow variable must be
NOTE
greater than the data resident in the high preset
(HSC:0.HIP) or an HSC error is generated.
Underflow (UNF)
Description Address
UNF - Underflow HSC:0.UNF
The UNF (Underflow) defines the lower count limit for the counter. If the
counter's accumulated value decrements past the value specified in this
variable, an underflow interrupt is generated. When the underflow
interrupt is generated, the HSC sub-system resets the accumulated value
to the overflow value and the counter then begins counting from the
overflow value (counts are not lost in this transition). The user can specify
any value for the underflow position, provided it is less than the overflow
value and falls between -2,147,483,648 and 2,147,483,647.
To load data into the underflow variable, the control program must toggle
(low to high) the Set Parameters (HSC:0.0/SP) control bit. When the SP bit
is toggled high, the data currently stored in the HSC function file is
transferred/loaded into the HSC sub-system.
Data loaded into the overflow variable must be greater
NOTE
than the data resident in the high preset (HSC:0.HIP) or
an HSC error is generated.
Using the High-Speed Counter
Data Format Type
long word (32-bit INT) control
Data Format Type
long word (32-bit INT) control
5-23
User Program Access
read/write
User Program Access
read/write
Publication 1762-RM001C-EN-P