TS80C54X2YYY-MICD Atmel Corporation, TS80C54X2YYY-MICD Datasheet - Page 32

• Manufacturer Part Number: TS80C54X2YYY-MICD
• Description: 8-bit CMOS Microcontroller 16/32 Kbytes ROM/OTP
• Manufacturer: Atmel Corporation

TS80C54X2/C58X2
TS87C54X2/C58X2
6.9 ONCE
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:
While the TS80C54/58X2 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.
32
Weak pull-up
Pull ALE low while the device is in reset (RST high) and PSEN is high.
Hold ALE low as RST is deactivated.
ALE
TM
Mode (ON Chip Emulation)
Weak pull-up
PSEN
Table 17. External Pin Status during ONCE Mode
Port 0
Float
Weak pull-up
Port 1
Weak pull-up
Port 2
Weak pull-up
Port 3
Rev. C - 15 January, 2001
XTAL1/2
Active