33742 datasheet(34/70 Pages) FREESCALE

34 / 70 page

Analog Integrated Circuit Device Data

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 350ms 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

At Step 2, the SBC is in Normal Request. Steps 3, 4, and 5

should be completed consecutively and within the 350ms

time period of the Normal Request mode. If not, the 33742

will go into Reset mode and enter Normal Request again.

Figure 15, page 34, illustrates debug mode selection.

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 350ms. 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 350ms 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

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

33742 数据表(PDF) 34 Page - Freescale Semiconductor, Inc

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