User guide

Order of events
The programmer executes a specific sequence of events in order to enter ‘Serial
Programming Mode’. If the selected target device requires a Vpp to be applied, this voltage
will be generated from the programmer. If the target device does not require a Vpp voltage,
the programmer will apply a continuous +5V voltage to the Vpp pin.
Action Description
1 User selects a programming operation
2 The programmer asserts the PROG_ACTIVE pin.
RESET pin remains tri-stated.
3 Programmer waits for period T1.
This time could be used for the target microcontroller to safely close down any
tasks such as writing to an external EEPROM.
4 Programmer asserts the PROG_RESET pin.
The target microcontroller enters the RESET state.
User code execution is halted.
5 Programmer waits for period T2.
6 Programmer switches on the Vpp generator circuit and connects the output of
the Vpp generator circuit to the PROG_VPP pin.
This applies the Vpp voltage to the target system.
7 Programmer waits for period T4.
This delay must be long enough to allow the Vpp voltage to reach and stabilise at
the specified value.
8 Programmer tri-states the PROG_RESET pin.
If a C/R RESET circuit is used on the target system, the RESET line will decay
exponentially as the RESET capacitor discharges through the RESET
resistance.
If a watchdog IC is used, the target circuit design must ensure that the
RESET line is released properly as this line is not driven by the programmer
when deasserted.
Target Settings continued
Figure 21
User Guide V1.10
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