AT43USB325E-AU Atmel, AT43USB325E-AU Datasheet - Page 105

• Manufacturer Part Number: AT43USB325E-AU
• Description: IC USB KEYBOARD CTRLR 64LQFP
• Manufacturer: Atmel
• Series: AVR®r

Specifications of AT43USB325E-AU

• Applications: Keyboard Controller
• Core Processor: AVR
• Program Memory Type: SRAM (16 kB)
• Controller Series: AT43USB
• Ram Size: 512 x 8
• Interface: SPI, 3-Wire Serial
• Number Of I /o: 42
• Voltage - Supply: 4.4 V ~ 5.25 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 64-LQFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

12. Errata Sheet
12.1
12.2
3355C–USB–4/05
Problem
Fix/Workaround
Errata (All Date Codes): Missed Watchdog Timer Reset
There is a synchronization problem between the watchdog clock and the AVR clock. Even
though the clock inputs to both the watchdog timer and the AVR core are generated through the
same crystal, the two clock sources are not going through the same PLL. The AVR is clocked at
12 MHz and the watchdog timer is clocked at 1MHz. The WDR (Watchdog Reset) instruction is a
one-clock-cycle instruction. As such, when a watchdog timer reset occurs due to a WDR, the
watchdog timer may miss the reset. This happens frequently if the AVR is clocked much faster
than the watchdog timer.
A workaround is to invoke the WDR repetitively to ensure that the watchdog timer will be able to
receive the reset signal. If the AVR runs at 12 MHz, the WDR command must be invoked four-
teen times back to back.
The following is the sample code for resetting and arming the watchdog timer, assuming the
AVR is running at 12 MHz:
To disarm and disable the watchdog, do the following:
Please note that if the AVR runs at 24 MHz, the WDR should be invoked twenty-six times.
asm ( "ldi r16,15\n WDR\n WDR\n WDR\n WDR\n WDR\n WDR\n WDR\n WDR\n WDR\n
WDR\n WDR\n WDR\n WDR\n out 0x21,r16 " );
asm ( "ldi r16,0x18\nldi r17,0x10\n\n out 0x21,r16\n out 0x21,r17 " );
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