Texas Instruments Incorporated

- 12 -

GC1012B 3.3V DIGITAL TUNER

SLWS138B

This document contains information which may be changed at any time without notice

3.2

SYNC MODE REGISTER

The sync mode register controls the action of the SS and AS sync strobes and how they affect the

chip’s internal timers, counters, and accumulators.

ADDRESS 4:

Sync Mode Register

BIT

TYPE

NAME

DESCRIPTION

0 (LSB)

R/W

SS_OFF

This bit disables the SS input.

1

R/W

AS_ON

Enables the accumulator sync AS. Normally the frequency accumulator will free

run. This bit causes the frequency accumulator to be initialized to the contents of

the frequency register when AS goes low. SS, instead of AS, will reset the

accumulator if AS_MUX is set and SS is not disabled by SS_OFF.

2

R/W

AS_MUX

Use SS for the accumulator sync. The AS input is ignored and the SS strobe is

used in its place when this bit is set and SS is not disabled by SS_OFF. (See

AS_ON and AS_FREQ).

3

R/W

LD_FREQ

Load the frequency register in the digital oscillator with the contents of the

frequency word registers. If left on, this bit will cause the frequency register to load

whenever a frequency word register is changed.

4

R/W

AS_FREQ

Enables the synchronous frequency load mode. When this bit is set and AS goes

low, the frequency register will be synchronously loaded with the contents of the

frequency control registers. SS, instead of AS, will load the frequency register if

AS_MUX is set and SS is not disabled by SS_OFF.

5

R/W

SS_DIAG

Enables diagnostic syncs. This bit routes the internal sync to the checksum

generator and to all accumulators and control counters within the chip. This forces

the chip to re-initialize at the start of every sync period. The internal sync period will

externally provided SS strobe.

6

R/W

TEST

is used to test chips at the factory.

7 (MSB)

R/W

SS_MUX

Use the sync counter’s terminal count strobe for the internal sync instead of the

sync input SS. The internal sync is output on the SO pin.

The operation of these control bits are illustrated in Figure 3.

Figure 3. Sync Controls

SYNC TO

CONTROL COUNTERS

DIAGNOSTIC SYNCS

SYNC FREQ

ACCUMULATOR

LOAD FREQ REGISTER

SYNC TO SO

SS_MUX

AS_FREQ

LD_FREQ

AS_ON

AS

AS_MUX

CK

TEST

SS

SS_OFF

SS_DIAG

1

0

1

0

1

0

COUNTER

PERIOD =

2

AND

OUTPUT CIRCUITS