AT43USB325

更新时间： 2024-11-28 22:39:15

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AT43USB325 数据手册

Errata (All Date Codes): Missed Watchdog Timer Reset

Problem

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 gener-

ated 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.

USB

Microcontrollers

Fix/Workaround

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 fourteen times back to back.

AT43USB320A

AT43USB325

AT43USB326

AT43USB351M

AT43USB353M

AT43USB355

The following is the sample code for resetting and arming the watchdog timer, assum-

ing the AVR is running at 12 MHz:

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 " );

To disarm and disable the watchdog, do the following:

asm ( "ldi r16,0x18\nldi r17,0x10\n\n out 0x21,r16\n out 0x21,r17 " );

Please note that if the AVR runs at 24 MHz, the WDR should be invoked twenty-six

times.

Errata Sheet

3469A–USB–4/04

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型号	品牌	获取价格	描述	数据表
AT43USB325_05	ATMEL	获取价格	Multimedia USB Keyboard Controller with Embedded Hub
AT43USB325E-AC	ATMEL	获取价格	Multimedia USB Keyboard Controller with Embedded Hub
AT43USB325E-AU	ATMEL	获取价格	Multimedia USB Keyboard Controller with Embedded Hub
AT43USB325M-AC	ATMEL	获取价格	RISC Microcontroller, 8-Bit, MROM, AVR RISC CPU, 12MHz, CMOS, PQFP64, 1.40 MM HEIGHT, PLAS
AT43USB326	ATMEL	获取价格	Missed Watchdog Timer Reset
AT43USB326_06	ATMEL	获取价格	Multimedia USB Keyboard Controller with Embedded Hub
AT43USB326-AC	ATMEL	获取价格	Multimedia USB Keyboard Controller with Embedded Hub
AT43USB326-AU	ATMEL	获取价格	Multimedia USB Keyboard Controller with Embedded Hub
AT43USB351M	ATMEL	获取价格	Missed Watchdog Timer Reset
AT43USB351M_04	ATMEL	获取价格	Full-speed/ Low-speed USB Microcontroller with ADC and PWM