AT89C51IC2-SLSCM datasheet(105/146 Pages) ATMEL

Part #	AT89C51IC2-SLSCM

Description	8-bit Flash Microcontroller with 2-wire Interface

PDF	146 Pages

Scroll/Zoom	100%

Manufacturer	ATMEL [ATMEL Corporation]

Direct Link	http://www.atmel.com

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105 / 146 page

105

AT89C51IC2

4301A–8051–01/04

ONCE(TM) Mode (ON

Chip Emulation)

The ONCE mode facilitates testing and debugging of systems using AT89C51IC2 with-

out removing the circuit from the board. The ONCE mode is invoked by driving certain

pins of the AT89C51IC2; the following sequence must be exercised:

•

Pull ALE low while the device is in reset (RST high) and PSEN is high.

•

Hold ALE low as RST is deactivated.

While the AT89C51IC2 is in ONCE mode, an emulator or test CPU can be used to drive

the circuit Table 82 shows the status of the port pins during ONCE mode.

Normal operation is restored when normal reset is applied.

Table 82. External Pin Status during ONCE Mode

(a) "Once" is a registered trademark of Intel Corporation.

ALE

PSEN

Port 0

Port 1

Port 2

Port 3

Port I2

XTALA1/2

XTALB1/2

Weak

pull-up

Weak

pull-up

Float

Weak

pull-up

Weak

pull-up

Weak

pull-up

Float

Active

AT89C51IC2-SLSCM Datasheet(PDF) 105 Page - ATMEL Corporation