Propeller Manual

Table Of Contents

2: Spin Language Reference – CTRA, CTRB

CTRA, CTRB

((PUB ┆ PRI))

CTRA

((PUB ┆ PRI))

CTRB

Returns: Current value of Counter A or Counter B Control Register, if used as a source

variable.

Explanation

CTRA and CTRB are two of six registers (CTRA, CTRB, FRQA, FRQB, PHSA, and PHSB) that affect the

behavior of a cog’s Counter Modules. Each cog has two identical counter modules (A and B)

that can perform many repetitive tasks. The

CTRA and CTRB registers contain the

configuration settings of the Counter A and Counter B Modules, respectively.

The following discussion uses

CTRx, FRQx and PHSx to refer to both the A and B pairs of each

Each of the two counter modules can control or monitor up to two I/O pins and perform

conditional 32-bit accumulation of the value in the FRQx register into the PHSx register on

every clock cycle. Each Counter Module has its own phase-locked loop (PLLx) which can be

used to synthesize frequencies from 64 MHz to 128 MHz.

With just a little configuration and in some cases a little maintenance from the cog, the

counter modules can be used for:

• Frequency synthesis

• Frequency measurement

• Pulse counting

• Pulse measurement

• Multi-pin state measurement

• Pulse-width modulation (PWM)

• Duty-cycle measurement

• Digital-to-analog conversion (DAC)

• Analog-to-digital conversion (ADC)

• And more.

For some of these operations the cog can set the counter’s configuration, via

CTRA or CTRB,

and it will perform its task completely independently. For others, the cog may use

WAITCNT to

time-align the counter’s reads and writes within a loop; creating the effect of a more complex

Propeller Manual v1.1 · Page 95