Clock Source Modes; Gtm External Signal Description - Freescale Semiconductor MPC8313E Family Reference Manual

Powerquicc ii pro integrated processor

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System Configuration

Super-cascaded mode: In this mode, all four 16-bit timers can be internally cascaded to form a

64-bit counter. When working in the super-cascaded mode, the cascaded GTRFR, GTCPR, and

GTCNR should be referenced with two 32-bit bus cycles.

Clock Source Modes

The clock input to the timer's prescaler can be selected from three sources:

The system clock

The system slow go clock (system bus clock internally divided by 16)

The corresponding TINx pin

Reference Modes

Each timer can be configured to count until a reference is reached and then either begin a new time count

immediately or continue to run. The FRR bit of the corresponding GTMRR selects each mode.

Free run reference mode. The corresponding timer count continues to increment after the reference

value is reached.

Reset reference mode. The corresponding timer count is reset immediately after the reference value

Capture Modes

Each timer has a 16-bit field in GTCPR, used to latch the value of the counter when a defined transition of

TINx is sensed by the corresponding input capture edge detector.

Normal gate mode enables the count on a falling edge of the TGATE pin and disables the count on

the rising edge of TGATE. This mode allows the timer to count conditionally, based on the state of

The restart gate mode performs the same function as normal mode, except it also resets the counter

on the falling edge of the TGATE pin. This mode has applications in pulse interval measurement

and bus monitoring.

This section provides an overview and detailed descriptions of the GTM signals.

There are four distinct external input timer capture signals (TIN1, TIN2, TIN3, and TIN4), four distinct

external input timer gate signals (TGATE1, TGATE2, TGATE3, and TGATE4), and four distinct external

timer output signals (TOUT1, TOUT2, TOUT3, and TOUT4). The GTM interface signals are defined in

MPC8313E PowerQUICC II Pro Integrated Processor Family Reference Manual, Rev. 3

Freescale Semiconductor

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