DSP56857 datasheet(392/662 Pages) FREESCALE

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Functional Description

5685X Digital Signal Controller User Manual, Rev. 4

14-6

Freescale Semiconductor

14.5 Functional Description

A sub block of TOD implements the scaler, seconds, minutes, hours and days counters. The

counters can be initialized with the current time when the TOD module is disabled (when

TODEN = 0).

14.5.1 Scaler

Depending upon the frequency of the clock fed to the TOD module, the appropriate value should

be written to the clock scaler load register to derive a 1Hz clock. The scaler counter is a 16-bit up

counter, counting from zero while less than the value specified in the clock scaler register. In

normal operation, the scaler counter increments with TOD_CLK input (frequency range from

1-65536 Hz) if TODEN = 1. The base (1Hz) clock is generated when the scaler counter wraps

and is used to clock the time-of-day counters and 1Hz interrupt.

14.5.2 Time Units

Time units (seconds, minutes, hours, days) are each implemented as counter/register pairs.

14.5.2.1 Time Counters

The time counters are a set of modulo counters that are clocked by the 1 Hz clock to maintain the

current time in seconds, minutes, hours and days. They count only when TOD EN = 1. These

counters maintain the time to the accuracy of the 1 Hz clock. They initialize to the current value

in the time registers at the first 1Hz clock (one second) after TODEN is set to 1 and advance each

second thereafter.

14.5.2.2 Time Registers

Time registers are provided to set and observe the corresponding counters. When TODEN is set

to 1, the registers capture the counter values two IP_CLK cycles after the 1Hz clock and are

readable but not writeable. When TODEN is set to 0, they will contain the current value of the

time counters and they may be read or written.

14.5.2.3 Time-of-Day Lock Bit

When set, the TOD Lock Bit disables the continuous transfer of time-of-day counter values to the

registers when TODEN is 1. This permits a read of each of the four time registers without the

possibility of an in-process advancement of time values. The TOD_LOCK bit should remain set

at 0 except while reading the time registers when TODEN = 1.

DSP56857 Datasheet(PDF) 392 Page - Freescale Semiconductor, Inc