SM5819AF

SEIKO NPC CORPORATION —14

External input data and external system clock output switching

(1) Switching to external input data

When SELEXT is switched LOW to HIGH, the PCM data output is immediately switched to external

input data.

PLRCK and PBCK are similarly switched immediately to EXILRCK and EXIBCK in through mode,

respectively, regardless of the DIRPCK setting.

(2) Switching to external system clock

The MCKOUT system clock output can be switched between MCK and EXIMCK using SELEXT, as

given below.

SELEXT = “L”: MCK output

SELEXT = “H”: EXIMCK output

Note that neither MCK nor EXIMCK clock should be stopped during the switching interval to prevent a

micro-pulse being generated when switching.

The switching interval lasts from when SELEXT changes state until both clocks have made 4 transitions.

During this interval, the LOW-level clock pulsewidth of the first clock is extended until the rising edge of

the second clock occurs.

When the switching interval ends, the unused clock may then be stopped.

Figure 2. MCK

→ EXIMCK switching

Figure 3. EXIMCK

→ MCK switching

MCK

EXIMCK

SELEXT

MCKOUT

(Switching time)

(MCK OFF)

(EXIMCK ON)

MCK

EXIMCK

SELEXT

MCKOUT

OFF

(Switching time)

(MCK ON)

(EXIMCK OFF)