TS80C52X2 Datasheet, PDF (30/54 Pages) TEMIC Semiconductors – 8-bit CMOS Microcontroller 0-60 MHz

TS80C52X2
6.8 ONCE Mode (ON Chip Emulation)
The ONCE mode facilitates testing and debugging of systems using TS80C52X2 without removing the circuit from
the board. The ONCE mode is invoked by driving certain pins of the TS80C52X2; the following sequence must
be exercised:
q Pull ALE low while the device is in reset (RST high) and PSEN is high.
q Hold ALE low as RST is deactivated.
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 15. 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
30
Rev. B - Jan. 25, 1999
Preliminary