Analog Integrated Circuit Device Data
34
Freescale Semiconductor
33742
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
DEBUG MODE: HARDWARE AND SOFTWARE DEBUG WITH THE 33742
When a SBC, and the MCU it serves, is used on the same printed circuit board, both the MCU software and the 33742
operation must be debugged concurrently. The following features permit system debugging by allowing the disabling of the SBC
internal software watchdog timer.
DEVICE POWER-UP, RESET PIN CONNECTED TO VDD
The VDD voltage is available when the 33742 power-up but the 33742 will not have received any SPI communication to
configure itself. Until set up by the system MCU, the 33742 will generate a reset every 350 ms until the part is configured. To
avoid continuous MCU hardware resets, the 33742’s RST pin can be connected directly to the VDD pin by a hardware jumper.
DEBUG MODES WITH SOFTWARE WATCHDOG DISABLED THOUGH SPI (NORMAL DEBUG, STANDBY
DEBUG, AND STOP DEBUG)
The software configurable watchdog can be disabled through the SPI. To set the watchdog disable while limiting the risk of
inadvertently disabling the watchdog timer during normal 33742 operation, it is recommended that the disable be done using the
following sequence:
Step 1–Power down the SBC.
Step 2–Power up the SBC. This sets the BATFAIL bit, allowing the 33742 to enter Normal Request mode.
Step 3–Write to the TIM1 sub register to allow the SBC to enter Normal mode.
Step 4–Write to the MCR register with data 0000. This enables the debug mode. Complete SPI byte is 0001 0000.
Step 5–Write to the MCR register normal debug. SPI byte is 0001 x101.
Important While in debug mode, the SBC can be used without having to clear the watchdog on a regular basis to facilitate
software and hardware debug.
Step 6–To leave the debug mode, write 0000 to the MCR register.
At Step 2, the SBC is in Normal Request. Steps 3, 4, and 5 should be completed consecutively and within the 350 ms time
period of the Normal Request mode. If not, the 33742 will go into Reset mode and enter Normal Request again.
Figure 15. Entering Debug Mode
When the SBC is operating in the debug mode and has been set into Stop Debug or Sleep mode, a wake-up causes the 33742
to enter the Normal Request mode for 350 ms. To avoid having the SBC generate an unwanted reset (enter Reset mode), the
next debug mode (Normal Debug or Standby Debug) should be configured within the 350 ms time window of the Normal Request
mode.
To avoid entering debug mode after a power-up, first read the BATFAIL bit (MCR read) and write 0000 into the MCR register.
Figures 16 and
17, page 35, show the detailed operation of the SBC once the debug mode has been selected.
VSUP
SPI
MCR (Step 4)
BATFAIL
VDD
Debug Mode
MCR (Step 5)
SPI: Read BATFAIL
MCR (Step 6)
33742 in Debug mode.
33742 not in Debug mode.
TIM1(Step 3)
No Watchdog
Watchdog ON