《Atmel AT89C系列单片机电路板设计指南》.pdf

Designing Boards with Atmel AT89C51, AT89C52, AT89C1051, and AT89C2051 for Writing Flash at In-Circuit Test Designing Boards with Recent improvements in chips and not been observed during board design, testers have made it possible for the it may not be possible for a tester to write Atmel Flash tester to begin taking over the role tradi- the chip’s flash memory, and the chip will tionally assigned to the PROM program- have to be written with a PROM pro- Microcontrollers mer. Instead of having a PROM pro- grammer before being installed on the grammer write nonvolatile memories board. There are four main ways to inter- before assembling the board, the in-cir- fere with the tester’s attempts to write cuit tester writes them during in-circuit the flash memory. The four Don’ts: Application testing operations. Many Teradyne Z18- • Don’t tie needed input pins to VCC or series testers are now in use loading ground; Note code into nonvolatile memories, micro- • Don’t tie needed input pins to outputs controllers and in-circuit programmable Microcontroller of other IC’s; logic devices. The purpose of this note is to explain how the Z18 approaches the • Don’t tie supervoltage input pins to writing task for Atmel AT89C series IC’s, components that won’t tolerate the so that designers of boards using these voltage; chips can get the best results.