COP8CCR9IMT7SLASHNOPB datasheet(82/111 Pages) TI1

82 / 111 page

COP8CBR9, COP8CCR9, COP8CDR9

SNOS535I – OCTOBER 2000 – REVISED MARCH 2013

www.ti.com

Table 5-27. WATCHDOG Service Window Select (continued)

Clock

Service Window

WDSVR

Monitor

for High Speed Mode

for Dual Clock & Low Speed Modes

Bit 7

Bit 6

Bit 0

(Lower-Upper Limits)

Clock Monitor Enabled

5.16.1 CLOCK MONITOR

The Clock Monitor aboard the device can be selected or deselected under program control. The Clock

Monitor is ensured not to reject the clock if the instruction cycle clock (1/tC) is greater or equal to 5 kHz.

This equates to a clock input rate on the selected oscillator of greater or equal to 25 kHz.

5.16.2 WATCHDOG/CLOCK MONITOR OPERATION

The WATCHDOG is enabled by bit 2 of the Option register. When this Option bit is 0, the WATCHDOG is

enabled and pin G1 becomes the WATCHDOG output with a weak pull-up.

The WATCHDOG and Clock Monitor are disabled during reset. The device comes out of reset with the

WATCHDOG armed, the WATCHDOG Window Select bits (bits 6, 7 of the WDSVR Register) set, and the

Clock Monitor bit (bit 0 of the WDSVR Register) enabled. Thus, a Clock Monitor error will occur after

coming out of reset, if the instruction cycle clock frequency has not reached a minimum specified value,

including the case where the oscillator fails to start.

The WDSVR register can be written to only once after reset and the key data (bits 5 through 1 of the

WDSVR Register) must match to be a valid write. This write to the WDSVR register involves two

irrevocable choices: (i) the selection of the WATCHDOG service window (ii) enabling or disabling of the

Clock Monitor. Hence, the first write to WDSVR Register involves selecting or deselecting the Clock

Monitor, select the WATCHDOG service window and match the WATCHDOG key data. Subsequent

writes to the WDSVR register will compare the value being written by the user to the WATCHDOG service

window value, the key data and the Clock Monitor Enable (all bits) in the WDSVR Register. Table 5-28

shows the sequence of events that can occur.

The user must service the WATCHDOG at least once before the upper limit of the service window expires.

The WATCHDOG may not be serviced more than once in every lower limit of the service window.

When jumping to the boot ROM for ISP and virtual E2 operations, the hardware will disable the lower

window error and perform an immediate WATCHDOG service. The ISP routines will service the

WATCHDOG within the selected upper window. The ISP routines will service the WATCHDOG

immediately prior to returning execution back to the user's code in flash. Therefore, after returning to flash

memory, the user can service the WATCHDOG anytime following the return from boot ROM, but must

service it within the selected upper window to avoid a WATCHDOG error.

The WATCHDOG has an output pin associated with it. This is the WDOUT pin, on pin 1 of the port G.

WDOUT is active low. The WDOUT pin has a weak pull-up in the inactive state. Upon triggering the

WATCHDOG, the logic will pull the WDOUT (G1) pin low for an additional 16–32 cycles after the signal

level on WDOUT pin goes below the lower Schmitt trigger threshold. After this delay, the device will stop

forcing the WDOUT output low. The WATCHDOG service window will restart when the WDOUT pin goes

high.

A WATCHDOG service while the WDOUT signal is active will be ignored. The state of the WDOUT pin is

not ensured on reset, but if it powers up low then the WATCHDOG will time out and WDOUT will go high.

The Clock Monitor forces the G1 pin low upon detecting a clock frequency error. The Clock Monitor error

will continue until the clock frequency has reached the minimum specified value, after which the G1 output

will go high following 16–32 clock cycles. The Clock Monitor generates a continual Clock Monitor error if

the oscillator fails to start, or fails to reach the minimum specified frequency. The specification for the

Clock Monitor is as follows:

1/tC > 5 kHz—No clock rejection.

Functional Description

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