78M6613 Data Sheet
DS_6613_018
An alternate solution using discrete components can be used. Figure 13 shows an implementation using
a shunt regulator and two transistors.
Figure 13: Reset Generator Based On TL431 Shunt Regulator
As long as V3P3 is below the 2.79V threshold set by the voltage divider of R1 and R2, U1 will not
conduct current, the base of Q2 will be at the same potential as its emitter, so Q1 will be turned off. With
no current flowing in the collector of Q2, the base of Q1 will be low, Q1 will be turned off, and RESET will
track V3P3. When the V3P3 rises above 2.79V, the TL431 starts to conduct, the base of Q2 is be pulled
low, turning on Q2. This drives the base of Q1 high, turning Q1 on and pulling RESET low. The inherent
turn-on and turn-off delays of the TL4313 provide the ~1µs delay required to ensure proper resetting of
the 78M6613.
3.7 Connecting the Emulator Port Pins
It is important to bring out the ICE_E pin to the programming interface in order to create a way
for reprogramming parts that have the Flash SECURE bit (SFR 0xB2[6]) set. Providing access to
ICE_E ensures that the part can be reset between erase and program cycles, which will enable
programming devices to reprogram the part. The reset required is implemented with a watchdog timer
reset (i.e. the hardware WDT must be enabled).
78M6613
ICE_E
V3P3
62Ω
E_RST
62Ω
E_RXTX
E_TCLK
62Ω
300 Ω
1000pF
Figure 14: External Components for the Emulator Interface
18
Rev. 1.1
TERIDIAN [ TERIDIAN SEMICONDUCTOR CORPORATION ]
