20-668-0011 Rabbit Semiconductor, 20-668-0011 Datasheet - Page 43

• Manufacturer Part Number: 20-668-0011
• Description: IC MPU RABIT3000A 55.5MHZ128LQFP
• Manufacturer: Rabbit Semiconductor

Specifications of 20-668-0011

• Processor Type: Rabbit 3000 8-Bit
• Speed: 55.5MHz
• Voltage: 2.5V, 2.7V, 3V, 3.3V
• Mounting Type: Surface Mount
• Package / Case: 128-LQFP
• Data Bus Width: 8 bit
• Maximum Clock Frequency: 55.5 MHz
• Operating Supply Voltage: 1.8 V to 3.6 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 55 C
• Number Of Programmable I/os: 56
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Features: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 316-1061

4.3.3 Watchdog Timer
The watchdog timer is enabled on reset with a 2-second timeout. Unless specific data are
written to WDTCR before that time expires, the processor will be reset. The watchdog
timer can be disabled by writing a sequence of two bytes to WDTTR as described in the
register description.
The watchdog timer also contains a special test mode that speeds up the timeout period by
clocking it with the peripheral clock instead of the 32 kHz clock. This mode can be
enabled by writing to WDTTR.
4.3.4 Secondary Watchdog Timer (Rabbit 3000A)
The secondary watchdog timer is disabled on reset, unless the reset occurs because the
primary watchdog timer times out while the secondary watchdog timer is enabled. The
BIOS provided by Rabbit Semiconductor in Dynamic C avoids this bug by disabling the
secondary watchdog on startup or reset by writing 0x005F to WDTCR. The following
steps explain how to use the secondary watchdog timer.
1. Write the vector to the interrupt service routine to the internal interrupt table.
2. Write the desired timeout period to SWDTR. This also enables the secondary watchdog
3. Restart the secondary watchdog timer by either writing the timeout period to SWDTR
If the secondary watchdog timer counts down to zero, a Priority 3 secondary watchdog
interrupt will occur. This interrupt request is cleared by writing a new timeout value to
SWDTR. A sample interrupt handler is shown below.
Chapter 4 System Management
timer.
or writing 0x005F to WDTCR.
secwd_isr::
push af
; determine why the interrupt occurred and take appropriate action
ld a, 0x40
ioi ld (SWDTR), a
pop af
ipres
ret
WDTCR Value
0x005A
0x0057
0x0059
0x0053
0x005F
Table 4-1. Watchdog Timer Settings
Restart watchdog timer with 2-second timeout.
Restart watchdog timer with 1-second timeout.
Restart watchdog timer with 500-millisecond timeout.
Restart watchdog timer with 250-millisecond timeout.
Restart the secondary watchdog timer.
; timeout period of 0x40/32kHz = 1.95ms
; clear the interrupt request
Effect
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