HMC7000 Series I/O Module Guide
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HMC7000 Series I/O Module Guide
83
Configuration of the HMC7000 Series High Speed Counters
Maple Systems’ HMC products have built-in High-Speed counters that link directly to specific inputs and outputs.
Specific registers and bits are predefined for setup and control of these counters. No logic is required to run the
counters, other than logic that may be used to configure and control the counters.
Two inputs on the module are used as the Triggers for the High-Speed counters, and two outputs are used as
the Done bits. The inputs support a maximum speed of 25 KHz.
The following bits and registers are associated with a High-Speed counter:
Register/ Bit
Description
Configuration
Register
The 16-bit register that controls how the High-Speed counter operates.
Bits 3-0 are used (see below)
Current Count
Register
The 32-bit register that counts the number of times that the Trigger has
transitioned. The specified register is the Least Significant Word (LSW); the next
consecutive register is the Most Significant Word (MSW).
Preset Register
The 32-bit register that defines the number of counts at which the Done bit will be
set (see description of Done Bit below). The specified register is the Least Significant
Word (LSW); the next consecutive register is the Most Significant Word (MSW).
Trigger Bit
The input bit that triggers the count. The counter will increment by one on each bit
transition. The counter can operate on a falling (default) or rising edge.
Enable Bit
The counter will not run unless this bit is set. If this bit is reset while the counter is
running, the current values will be maintained, but the Trigger bit will have no
effect. The Done bit is reset if the Enable bit is reset. If the Current Count value is
greater than or equal to the Preset value, the Done bit is set after the Enable bit is
set again.
Reset Bit
When this bit goes from false to true, the current count will reset to 0 and the Done
bit is reset. The reset occurs even when the Enable bit is reset. The reset is
accomplished by an internal bit or a physical input.
Done Bit
The physical output that turns on when the Current Count is equal to or greater than
the Preset value. The bit remains set until the Reset bit goes true, even if the
counter counts beyond the preset. If the Enable bit is reset, the Done bit will reset.
If the Enable bit is set while the Current Count is equal to or greater than the Preset,
the Done bit is set.
