TS83C51RB2-VCKB View Datasheet(PDF) - Atmel Corporation

Part Name

Description

Manufacturer

TS83C51RB2-VCKB

High Performance 8-bit Microcontrollers

Atmel Corporation 

TS80C51RA2/RD2

TS83C51RB2/RC2/RD2

TS87C51RB2/RC2/RD2

6.11. ONCETM Mode (ON Chip Emulation)

The ONCE mode facilitates testing and debugging of systems using TS80C51Rx2 without removing the circuit

from the board. The ONCE mode is invoked by driving certain pins of the TS80C51Rx2; 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 TS80C51Rx2 is in ONCE mode, an emulator or test CPU can be used to drive the circuit Table 26.

shows the status of the port pins during ONCE mode.

Normal operation is restored when normal reset is applied.

Table 25. External Pin Status during ONCE Mode

ALE

Weak pull-up

PSEN

Weak pull-up

Port 0

Float

Port 1

Weak pull-up

Port 2

Weak pull-up

Port 3

Weak pull-up

XTAL1/2

Active

48

Rev. C - 06 March, 2001

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