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Hot on the heels of the new PICkit 4 comes the Snap Debugger/Programmer, and it’s a fraction of the price of a PICkit 4. So how does it compare? Read on and see. Review by Tim Blythman ICROCHIP SNAP DEBUGGER/PROGRAMMER Y ou’d probably recall our review of the PICkit 4 in the September 2018 issue (siliconchip.com. au/Article/11237). We noted that the PICkit 4 is faster than its predecessors, both for programming and debugging. Clones of the PICkit 2 and PICkit 3 are both in circulation, and given that Microchip has open-sourced the designs of both, the clones appear to work similarly; there is no reason for them to be significantly different to the originals. Either of these can be had for around $20 from many online sellers. The Snap is made by Microchip and appears to be selling at a similar price to the PICkit 2 and PICkit 3 clones, so it’s worthwhile comparing them. Microchip Direct (Microchip’s online store) sells the PICkit 4 for US$47.95, siliconchip.com.au while the Snap is US$14.95. The Snap Debugger/Programmer is based on the same Atmel SAM E70 32-bit MCU and has the same 8-pin header as the PICkit 4, although it’s somewhat less complex, which is how Microchip can reduce the cost compared to the PICkit 4. For a start, there is no enclosure; all you get is a bare PCB populated with Australia’s electronics magazine components. But we found a link on the Digi-Key website to download a set of 3D printable case files, at: www. thingiverse.com/thing:3074301 We’ll have more on that case later. Also, the PCB is much smaller than even the PICkit 2, let alone the PICkit 4. Partly this is because it lacks a microSD card socket, so presumably, the Programmer-To-Go function is not available. There is a QR code stuck to the top of the main IC. It leads you to information on the Snap, at this link: siliconchip. com.au/link/aanq First use We are currently using MPLAB X version 5.05 (on Windows 10; Windows 7, macOS and some Linux variants are also supported). This is the May 2019  83 minimum version required to use the Snap, so we didn’t have to install any new software. We then tried to program a PIC32MX170 chip (on a Micromite BackPack), but this failed. It turns out that the Snap Debugger/ Programmer is not capable of providing power to the target, even though there is a checkbox for this in the power settings page. Once we realised this, we connect an external DC supply to the board and were then able to program the PIC32MX170. The programming speed appears comparable to the PICkit 4, which we expected based on them using a similar SAM E70 processor. A further peruse indicated that highvoltage programming is not supported either, which rules out its use with many ‘legacy’ PICs such as the (still in production) PIC16F84A. So it seems that the main reason for the Snap being so much cheaper is that they’ve left off some of the features of the PICkit, some of which are mainly for convenience (eg, providing power to the target processor) while others are only needed for use with older PICs. A closer look On this basis, we decided to take a closer look at Microchip’s information sheet to see what else sets the Snap apart from the PICkit 4. It can be downloaded from siliconchip.com. au/link/aanp The manual mentions that the emergency recovery jumper is unpopulated; you activate it by shorting the header pins, while on the PICkit 4, a tactile button is provided for this function. There is also a comparison table between the two programmers (see above right). In particular, the programmable power options are missing on the Snap, as are the configurable pull-ups for the programming pins. There is an ‘interface comparison’ which notes that practically the same programming interfaces are available, with the proviso that only the low voltage version is available for some chips. It also confirms that there is no programmer-to-go feature, and that the Snap is not intended to be a production programmer, while the PICkit 4 is. The PICkit 4 is also claimed to support all Microchip flash-based MCUs, while the Snap supports most. This is slightly vague, but makes it clear that the Snap is not a direct sub84 Silicon Chip Using the IPE (integrated programming environment) version 5.05 with the Snap programmer. It looks similar to when using the PICkit 4; in fact, the only visible difference is the programmer name. stitute for the PICkit 4. Take it for a spin Once we’d cleared up the issue of powering the target, we tried a few programming and debugging exercises using many PIC32 devices, including PIC32MX170s and PIC32MX470s in various Micromites, as well as the PIC32MX270 in the February 2019 USB Mouse and Keyboard Interface for Micros (siliconchip.com.au/ Article/11414). The speed of working with Snap seemed to be on par with the PIC kit, so if you only need to work with PIC32 devices, the Snap could be a good choice. We checked the device support list for MPLABX 5.10, and it appears that the Snap now supports most (but not quite all) PIC32 devices to some extent. Programming 8-bit & 16-bit PICs Next, we tried the PIC16F1455, which has appeared most notably in the May 2017 Microbridge project (siliconchip.com.au/Article/10648) and as the USB/serial interface of the Australia’s electronics magazine Micromite Backpack V2 (May 2017; siliconchip.com.au/Article/10652) and the USB Digital Interface Module (November 2018; siliconchip.com.au/ Article/11299). Initially, we tried a chip that had already been programmed for the Digital Interface Module, but could not get the Snap to communicate with it. Using a PICkit 4, we found that the LVP (low voltage programming) option on that chip had been disabled. After using the PICkit 4 to reset this, we found that Snap could happily read and program the 16F1455. As noted earlier, the Snap cannot do high-voltage programming. Other 8-bit PICs such as the 12F617 and 16F84 require high voltage programming, so we did not try to program these. As expected, the device support list (for both MPLABX 5.05 and 5.10) indicates that these devices are not supported by the Snap tool. Give me power We note that the Snap board has pads for 3.3V, 5V and GND easily accessible, so it may be possible to rig siliconchip.com.au There’s not much to the Snap PCB. At left there are a few support ICs, including an MCP1727 voltage regulator. At centre is the SAM E70 processor, and at right is the I/O pin interface circuitry. In comparison to the PICkit 4, it lacks high voltage circuitry and target power supply amongst others. up a jumper wire to provide power to the target board if necessary. These pads are next to a DFN-8 chip marked as U5, which is an MCP1727 voltage regulator. The MCP1727 is capable of 1.5A, although its power dissipation while dropping 5V down to 3.3V would bring it close to its thermal limit. In any case, the typical 500mA limit of the USB is sure to come into play long before 1.5A is reached. We 3D printed one of the Digi-Keydesigned cases, just to protect the unit from damage. Before we fitted the case, we noted that the board appears to get quite warm, even when idle. As it is, we’ve left the lid off the case for now, as we don’t want it to overheat. There appear to be some other spare pads around the board, including a pair of test points, another pair marked RX0 and TX0, a small pitch 8-way header marked J2, a small pitch 2-way header marked J3 and a row of five headers marked for synchronous serial data of some sort. None of these are noted in the information sheet, so we can only speculate as to their purpose; they may be for some as yet, unreleased feature. programming. Part support is still in progress. It appears that many parts are still only at the preliminary or beta stage of support, including those we have tested. Nonetheless, we found that they worked fine for programming and sim- ple debugging. If you are only working with 32-bit PICs, the Snap appears to be an economical option which provides practically all the upsides of the PICkit 4, as long as you can live with providing power to your target micro independently of the programmer. If you plan to use other devices, we would not recommend it. There are a small number of 8-bit devices that it supports, such as the 16F1455, although some of these parts offer high voltage and low voltage programming. This means the Snap programmer would work if the chip is configured with low voltage programming disabled. But keep in mind that the low-voltage programming can typically only be disabled when using a high-voltage capable programmer, so you should be safe to use these parts with the Snap. Overall, it’s ideal as an economical first programmer, or as a second device to carry with your laptop or notebook, although we would recommend taking a good look at the device support list before making a decision. SC Our verdict The Snap Debugger/Programmer is clearly an economy device intended to be used with newer microcontrollers, especially as it cannot work at all with older devices that require high-voltage siliconchip.com.au MPLAB SNAP vis MPLAB PICkit 4 comparison. Australia’s electronics magazine May 2019  85