How The Programmer Measures The Target Vcc - Equinox Systems ISPnano I Series User Manual

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Datasheet of ISPNANO S3 KIT - ISP PORTABLE PROGRAMMER
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The voltage is then applied to the input of the 'Voltage Regulator Circuit' on the Target
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System.
The 'Voltage Regulator Circuit' on the Target System then generates the supply rail(s)
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voltage(s) for the device(s) to be programmed – V_TARTGET_REG in the above diagram.
This generated voltage is the voltage that the device(s) to be programmed are actually running
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at and is known as the 'Target Vcc (TVCC)'. The voltage is usually in the range of 1.6 – 5.0V
for most programmable devices.
The programmer can measure the 'Target Vcc (TVCC)' to make sure that this voltage is
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within the limits specified for the Target Board.
The Target System requires that a 'POWER_GROUND' connection is made from the
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GROUND of the Target System back to the star-connected GROUND connection of the power
supply / test fixture.
Important note:
If the programmer is switching an 'External power supply' to the Target System and then
measuring the Target Voltage (on the TVCC pin) then the programmer must wait for the 'Target
Voltage' to stabilise at its final value after switching the 'External power supply' on before
measuring the voltage.

4.5.2 How the programmer measures the Target Vcc

When the programmer is NOT controlling Target Power but instead is switching an 'External Supply'
to the Target System, it is still possible for the programmer to measure and check the 'Target
Voltage'.
This is how the programmer handles switching on of the 'External Vcc'....
The operator must manually switch on the EXTERNAL VOLTAGE (V_EXT) to the 'DC-
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EXT' connector.
Start the programming project or press <Power up> in EDS mode
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Programmer switches on the 'External VCC Switch' and sets an internal timer to t=0.
The regulator / power supply on the Target System will then switch on and start to charge
on any on-board capacitance such as reservoir capacitors.
The programmer then waits for the 'Voltage Settle time' to elapse which gives time for the
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any capacitance to charge up and the 'Target Voltage' to settle to its final value.
The programmer then starts to check that the 'Target Voltage' measured on the TVCC pin
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is within the limits specified in the project. If it is not, then an 'Error 64 – Target voltage is
outside limits' is immediately generated.
If the voltage is within limits, the programmer will continue to check 'Target Voltage' is
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within limits until the 'PSU_OUT delay' has elapsed. This ensures that the voltage is
definitely stable (ie not fluctuating) before the programming operation commences.
Example:
Let's say the power supply on the Target System has a 24V input voltage and a 3.3V output voltage.
The time taken for the 3.3V supply to reach 3.3V is approximately 600ms after the 24V supply has