C8051F960-B-GM Datasheet, PDF (314/492 Pages) Silicon Laboratories – Ultra Low Power 128K, LCD MCU Family

C8051F96x
wise, then the counter clockwise counter 1 value represents the cumulative back-flow. Firmware may use
the back-flow counter with the corresponding comparator to implement a back-flow alarm. The clock-wise
sequence is (LL-HL-HH-LH), and the counter clock-wise sequence is (LL-LH-HH-HL). (For this sequence
LH means PC1 = Low and PC0 = High.)
Firmware cannot write to the counters. The counters are reset when PC0MD is written and have their
counting enabled when the PC0MD[7:6] mode bits are set to either single, dual, or quadrature modes. The
counters only increment and will roll over to 0x000000 after reaching 0xFFFFFF. For single mode, the PC0
input connects to counter 0. In dual mode, the PC0 input connects to counter 0 while the PC1 input con-
nects to counter 1. In Quadrature mode, clock-wise counts are sent to counter 0 while counter clock-wise
counts are sent to counter 1.
25.2. Reed Switch Types
The Pulse Counter works with both Form-A and Form-C reed switches. A Form-A switch is a Normally-
Open Single-Pole Single-Throw (NO SPST) switch. A Form-C reed switch is a Single-Pole Double-Throw
(SPDT) switch. Figure 25.3 illustrates some of the common reed switch configurations for a single-channel
meter.
The Form-A switch requires a pull-up resistor. The energy used by the pull-up resistor may be a substantial
portion of the energy budget. To minimize energy usage, the Pulse Counter has a programmable pull-up
resistance and an automatic calibration engine. The calibration engine can automatically determine the
smallest usable pull-up strength setting. A Form-C switch does not require a pull-up resistor and will pro-
vide a lower power solution. However, the Form-C switches are more expensive and require an additional
wire for VBAT.
Form A
VBAT
PC0
pull-up required
Form C
VBAT
no pull-up
PC0
Figure 25.3. Reed Switch Configurations
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