TS80C54 ATMEL [ATMEL Corporation], TS80C54 Datasheet - Page 33

• Manufacturer Part Number: TS80C54
• Description: 8-bit CMOS Microcontroller 16/32 Kbytes ROM/OTP
• Manufacturer: ATMEL [ATMEL Corporation]

13. ONCE
4431E–8051–04/06
TM
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:
While the TS80C54/58X2 is in ONCE mode, an emulator or test CPU can be used to drive the
circuit
Normal operation is restored when normal reset is applied.
Table 13-1.
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
Table 13-1
External Pin Status during ONCE Mode
Weak pull-up
shows the status of the port pins during ONCE mode.
PSEN
Port 0
Float
Weak pull-up
Port 1
Weak pull-up
Port 2
AT/TS8xC54/8X2
Weak pull-up
Port 3
XTAL1/2
Active
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