TS87C52X2 ATMEL Corporation, TS87C52X2 Datasheet - Page 28

• Manufacturer Part Number: TS87C52X2
• Description: 8-bit Microcontroller 8 Kbytes Otp
• Manufacturer: ATMEL Corporation

ONCE
Emulation)
28
TM
TS8xCx2X2
Mode (ON Chip
The ONCE mode facilitates testing and debugging of systems using TS80C52X2 with-
out removing the circuit from the board. The ONCE mode is invoked by driving certain
pins of the TS80C52X2; the following sequence must be exercised:
•
•
While the TS80C52X2 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 16. External Pin Status during ONCE Mode
Weak pull-
Pull ALE low while the device is in reset (RST high) and PSEN is high.
Hold ALE low as RST is deactivated.
ALE
up
Weak pull-
PSEN
up
Port 0
Float
Weak pull-
Port 1
up
Weak pull-
Port 2
up
Weak pull-
Port 3
up
4184E–8051–09/02
XTAL1/2
Active