AT87C54X2-3CSUL View Datasheet(PDF) - Atmel Corporation

Part Name

Description

Manufacturer

AT87C54X2-3CSUL

8-bit CMOS Microcontroller 16/32 Kbytes ROM/OTP

Atmel Corporation 

AT/TS8xC54/8X2

13. ONCETM Mode (ON Chip Emulation)

The ONCE mode facilitates testing and debugging of systems using TS80C54/58X2 without

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

TS80C54/58X2; 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 TS80C54/58X2 is in ONCE mode, an emulator or test CPU can be used to drive the

circuit Table 13-1 shows the status of the port pins during ONCE mode.

Normal operation is restored when normal reset is applied.

Table 13-1. 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

33

4431E–8051–04/06

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