Datasheet

Analog Integrated Circuit Device Data
Freescale Semiconductor 44
MC34708
Functional Block Description
is attached by de-asserting the STANDBY pin and waking up for a period to see if a device is attached and then re-asserting
Standby if a device has not been detected. If a device has been detected then the software can bring up the appropriate
application etc.
Note the STANDBY pin is programmable for Active High or Active Low polarity, and decoding of a Standby event will take into
account the programmed input polarity associated with each pin. For simplicity, Standby will generally be referred to as active
high throughout this document, but as defined in
Table 29, active low operation can be accommodated. Finally, since STANDBY
pin activity is driven asynchronously to the system, a finite time is required for the internal logic to qualify and respond to the pin
level changes.
The state of the STANDBY pin only has influence in On mode, and are therefore it is ignored during start up and in the Watchdog
phase. This allows the system to power up without concern of the required Standby polarities since software can make
adjustments accordingly as soon as it is running.
A command to transition to one of the low power Off states (User Off or Memory Hold, initiated with USE-ROFFSPI=1) redefines
the power tree configuration based on SWxMODE programming, and has priority over Standby (which also influences the power
tree configuration).
7.5.3.8.2 Standby Delay
A provision to delay the Standby response is included. This allows the processor and peripherals, some time after a Standby
instruction has been received, to terminate processes to facilitate seamless Standby exiting and re-entrance into Normal
operating mode.
A programmable delay is provided to hold off the system response to a Standby event. When enabled (STBYDLY = 01, 10, or
11), STBYDLY will delay the STANDBY initiated response for the entire IC until the STBYDLY counter expires.
Note that this delay is applied only when going into Standby, and no delay is applied when coming out of Standby. Also, an
allowance should be accounted for synchronization of the asynchronous Standby event and the internal clocking edges (up to a
full 32
kHz cycle of additional delay).
Table 29. Standby Pin and Polarity Control
STANDBY (Pin) STANDBYINV (SPI bit) STANDBY Control
(43)
0 0 0
0 1 1
1 0 1
1 1 0
Notes
43. STANDBY = 0: System is not in Standby STANDBY = 1: System is in Standby
Table 30. Delay of STANDBY- Initiated Response
STBYDLY[1:0] Function
00
No Delay
01
One 32 k period (default)
10
Two 32 k periods
11
Three 32 k periods