The Counter Timer Module is actually a collection of separate timer modules with specialized capabilities. Most of these are independent single-action or double-action counter/timers that connect to a bidirectional I/O pin on the CF1. The remaining modules cooperate to provide the four timebases used by the CTMs to perform their work.

A Single Clock Prescaler Submodule (CPSM) feeds one Free-Running Counter Submodule (FCSM) and three Modulus Counter Submodules (MCSM) with six individually selectable clocks derived from the CPU system clock. The FCSM and MCSM modules drive the four timebases from one of these clocks or from an external clock. The FCSM has a fixed modulus of 65536, while the MCSMs have loadable modulus registers and load inputs for greater flexibility.

Single Action Submodules: The CTM has eight SASMs, six connect to I/O pins from the CF1, while the other two are used internally by the CF1 for simple I/O. Each SASM can perform one of the following functions:

• Input Capture: Capture the timebase on either edge of the I/O pin and optionally generate an interrupt.
• Output Port: Set or clear the I/O pin.
• Output Compare: Set or clear the I/O pin on a timebase match and optionally generate an interrupt.
• Output Compare and Toggle: Toggle the I/O pin on a timebase match and optionally interrupt.

Double Action Submodules: The CTM has eleven DASMs which all connect to I/O pins from the CF1. In addition to the functions listed for the SASMs, each DASM can perform one of the following functions:

• Input Pulse Width Measurement: Measure the time between leading and falling edges of the I/O pin and optionally generate an interrupt on completion.
• Input Period Measurement: Measure the time between two successive leading or falling edges of the I/O pin and optionally generate an interrupt on completion.
• Output Pulse Width Modulation: Generate a pulse width modulated waveform with selectable resolutions of 7, 9, 11, 12, 13, 14, 15, or 16 bits.

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