1.8V and 2.5VBuffered Isolated Dual-Chip Setup
Low Voltage Configuration
NSPSP cannot run at voltages below 3.3V. Therefore, if your PIC runs at voltage less than 3V, special arrangements are necessary to organize interface between PIC and NSDSP. One of the methods is to use level translators between PIC and NSDSP. Other method is to to temporarily elevate voltage to 3.3V when USB is connected.
Level shifters or isolators is the most straightforward solution. NSDSP may be powered by USB. 5V USB power can be used to directly power NSDSP running at 5V. While USB cable is unplugged, NSDSP is left completely un-powered and therefore does not consume any board power.
When designing level shifters, you need to make sure that none of the NSDSP pins is driven high while the power is disconnected.
Temporarily elevating voltage
Other method is temporarily elevating board voltage to 3.3V when USB cable is connected. All PIC devices can tolerate 3.3V. You need to make sure that other component on the board can tolerate elevated voltages too.
When USB cable is disconnected, you can disconnect the power from NSDSP too. This is the best solution for power conservation, however, you need to make sure that none of the NSDSP pins is driven high while the power is disconnected.
Alternatively, you can keep NSDSP powered at a lower voltage. However, if the voltage is less than approximately 3V, NSDSP will fall into a state of brown-out reset, which consumes considerably more power than regular sleep mode - about 200µA.
Many PIC devices, when run at lower voltages, cannot perform bulk erase. Therefore, they can only be programmed using special algotithms which avoid bulk erase operations. Such algorithms are usually considerably slower than regular algorithms, and NSDSP programmer will not use them unless you explicitly specify that the target voltage is below the bulk erase threashold. If you don't specify the target voltage, NSDSP will apply regular algorithms and programming will fail.
When programming at voltages below 3V, you must explicitly specify the target voltage in your programming software settings.
Many PIC devices cannot be programmed at lower voltages at full speed. NSDSP does not automatically reduce speed when programming at lower voltages. If you are getting errors, you may need to lower programming voltage to 4MHz, 3MHz, or lower.
When programmed at low voltages, many PIC devices may have other limitations. Due to these limitations, it may be impossible to program or debug PIC devices running at voltages below bulk erase threshold. For more details, find your PIC in the list of supported devices and make sure it supports all the operations you intend to perform.
© 2007-2017 Northern Software Inc. All Rights Reserved.