Once Mode; Entering And Exiting Once Mode - Intel 8XC196K Series User Manual

For example, assume that the oscillator needs at least 12.5 ms to discharge (T
is 2.5 V, and the discharge current is 200 µA. The minimum C
×
0.0125 0.0002
------------------------------------------ -
C
=
1
2.5
When using an external oscillator, the value of C
powerdown. For example, a 100 pF capacitor discharges in 1.25 µs.
×
C V
1 t
----------------- -
T
= =
DIS
I

14.5 ONCE MODE

On-circuit emulation (ONCE) mode isolates the device from other components in the system to
allow printed-circuit-board testing or debugging with a clip-on emulator. During ONCE mode,
all pins except XTAL1, XTAL2, V
mode, RESET# must be held high or the device will exit ONCE mode and enter the reset state.
Tables in Appendix B list the reset states of the pins (see Table B-8 on page B-20 for the
8XC196Kx, Table B-9 on page B-21 for the 8XC196Jx, or Table B-10 on page B-22 for the
87C196CA).

14.5.1 Entering and Exiting ONCE Mode

Holding the ONCE# signal low during the rising edge of RESET# causes the device to enter
ONCE mode. To prevent accidental entry into ONCE mode, we highly recommend configuring
this pin as an output. If you choose to configure this pin as an input, always hold it high during
reset and ensure that your system meets the V
ent entry into ONCE mode. Table 14-3 shows the ONCE# pin multiplexing for each device in the
8XC196Kx, Jx, and CA product families.
Exit ONCE mode by asserting the RESET# signal and allowing the ONCE# pin to float or be
pulled high. Normal operations resume when RESET# goes high.
1 µF
=
10
–
× ×
1.0 10 2.5
1.25 µs
------------------------------------------ -
=
0.0002
, and V
SS
Table 14-3. ONCE# Pin Alternate Functions
Device ONCE# Alternate Functions
8XC196CA P2.6/HLDA#
8XC196J x
P2.6/HLDA#
8XC196KQ, KR P5.4/SLPINT
8XC196KS, KT P2.6/HLDA#
SPECIAL OPERATING MODES
capacitor size is 1 µF.
1
can be very small, allowing rapid recovery from
1
are weakly pulled high or low. During ONCE
CC
specification (see datasheet) to prevent inadvert-
IH
= 12.5 ms), V
t
DIS
14-9