<p>In theory, you can; but, you may need those pins to attach an external programmer to bring your system back to life when playing around with the code.</p>

<p>Here are a couple of articles that could help if you still want to pursue that path:</p>

<ul>
<li><a href="https://electronics.stackexchange.com/questions/83108/can-spi-programmer-interfere-with-other-components-on-same-pins">Can SPI programmer interfere with other components on same pins?</a></li>
<li><a href="http://www.avrfreaks.net/forum/can-i-reuse-isp-pins-other-taskstarget-atmega164p" rel="nofollow noreferrer">Can I reuse ISP pins for other tasks?(Target: Atmega164p)</a></li>
</ul>

<p>Another option (the one I chose) is to just buy a RAMPS board set.  I got one on ebay for $19 and it have lots of more options for IO.  That way you can play and still go back and plug in your stock Melzi and print whenever you need it.</p>

<p>I got all this for $40 - boards, display, cables, power supply, and even shipping
<a href="https://i.sstatic.net/KKtgp.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/KKtgp.jpg" alt="enter image description here"></a></p>

<p>Here is a really nice detailed description of <a href="http://beginner3dprinter.com/" rel="nofollow noreferrer">converting a Duplicator i3 from Melzi to RAMPS</a>.  The process would likely be very similar for your printer.</p>

<p>The biggest challenge will likely be setting up the firmware</p>

<p>BTW, what printer did you get?</p>

CC BY-SA 4.0
2018-11-05T00:29:52.300Z
@markshancock, Repetier is the firmware shipped with the Maker Select (Wanhao rebranded). Repetier is FAR from dormant, and, frankly, has better bed-leveling.
Mark Ward
CC BY-SA 4.0
2018-11-16T18:55:25.240Z
@MarkWard Comparing the two firmwares on GitHub [Repetier](https://github.com/repetier/Repetier-Firmware) has 39 contributors and 999 commits (10 in the last 6mo) where [Marlin](https://github.com/MarlinFirmware/Marlin) has 415 contributors and 10,196 commits (437 in the last 6mo)
markshancock
CC BY-SA 3.0
2017-05-07T21:35:56.663Z
Fantastic answer! I ended up getting the Monoprice Maker Select v2.1 back in November. Couldn't beat the price and I saw it had a very large community of support. Made me really happy to see it's all parts that I've worked with and used before (Arduino and components).
Rincewind
CC BY-SA 3.0
2017-05-08T02:17:39.823Z
I have a Tronxy X3.  My printer has Repetier Firmware.  I have found it on GitHub; but, that code base seems dormant.  Marlin Firmware has a very active Open Source development (https://github.com/MarlinFirmware).  I look forward to playing with the code and it looks like Marlin would be a better place to do that.  It appears that either firmware will run the printer well.
markshancock
CC BY-SA 3.0
2017-05-08T17:17:36.900Z
I like the simplicity of that design. No frills, no additional things to get in the way, just all that is needed to make it work. It looks like it has a rather large build space, too. I haven't seen too many people with a Tronxy--what do you think of it?
Rincewind
CC BY-SA 3.0
2017-05-12T22:35:53.630Z
@Rincewind I like the X3; but, it is my first printer so I don't have much to compare it to.  The one thing I can say for sure is that it would likely not be a good option for someone that doesn't like fiddling with things.  It does have a few issues; but, there is a strong maker community around it so there are are fixes for all the issues.  The reason I wanted is because I wanted to fiddle and the open design makes that easy to do.  I am very happy with the printer and have not had a print fail yet.
markshancock
CC BY-SA 3.0
2017-05-07T20:55:27.000Z
2017-05-12T03:09:01.907Z
2017-05-12T03:09:01.907Z
markshancock
<p><strong>Background:</strong> <em>I have many years of experience with AVR and ARM Cortex PLCs and I feel very comfortable using them in projects but I am not an EE or SE. So, if I make a mistake or misunderstand something, keep that in mind. Thanks.</em></p>

<p>I cracked open the case on my Maker Select v2.1 and I noticed that I have a 2x3 header that is labeled ISP. This is fairly standard for the AVR PLCs and the Melzi board that I have uses the ATMEGA1284P.</p>

<p>I have asked at numerous forums and nobody seems to really know the answer (the downside to RepRap--people use but don't fully understand).</p>

<p>I'm wondering if I can tweak the Repetier firmware (I'm using the stock version 0.91) to use the ISP headers as a standard SPI bus. It has the SCK, MOSI, and MISO pins but it doesn't have the SS pin.</p>

<p>What I want to do is put a port expander on the SPI bus and break out additional usable GPIOs.</p>

<p>So, is there a hardware limitation or any other reason why I wouldn't be able to repurpose the ISP headers into an SPI bus?</p>

<reprap><repetier>
Can I repurpose the ISP pins in the lower right corner of the Melzi board?
Rincewind
# Can I repurpose the ISP pins in the lower right corner of the Melzi board?

(Asked by: username_0 on 2017-05-07)

**Background:** *I have many years of experience with AVR and ARM Cortex PLCs and I feel very comfortable using them in projects but I am not an EE or SE. So, if I make a mistake or misunderstand something, keep that in mind. Thanks.*

I cracked open the case on my Maker Select v2.1 and I noticed that I have a 2x3 header that is labeled ISP. This is fairly standard for the AVR PLCs and the Melzi board that I have uses the ATMEGA1284P.

I have asked at numerous forums and nobody seems to really know the answer (the downside to RepRap--people use but don't fully understand).

I'm wondering if I can tweak the Repetier firmware (I'm using the stock version 0.91) to use the ISP headers as a standard SPI bus. It has the SCK, MOSI, and MISO pins but it doesn't have the SS pin.

What I want to do is put a port expander on the SPI bus and break out additional usable GPIOs.

So, is there a hardware limitation or any other reason why I wouldn't be able to repurpose the ISP headers into an SPI bus?

**Tags:** reprap, repetier


---

## 1 answers

### Answer by username_1 on 2017-05-07. Score: 6 | Accepted answer

In theory, you can; but, you may need those pins to attach an external programmer to bring your system back to life when playing around with the code.

Here are a couple of articles that could help if you still want to pursue that path:

* [Can SPI programmer interfere with other components on same pins?](https://electronics.stackexchange.com/questions/83108/can-spi-programmer-interfere-with-other-components-on-same-pins)
* [Can I reuse ISP pins for other tasks?(Target: Atmega164p)](http://www.avrfreaks.net/forum/can-i-reuse-isp-pins-other-taskstarget-atmega164p)

Another option (the one I chose) is to just buy a RAMPS board set. I got one on ebay for $19 and it have lots of more options for IO. That way you can play and still go back and plug in your stock Melzi and print whenever you need it.

I got all this for $40 - boards, display, cables, power supply, and even shipping
[![enter image description here](https://i.sstatic.net/KKtgp.jpg)](https://i.sstatic.net/KKtgp.jpg)

Here is a really nice detailed description of [converting a Duplicator i3 from Melzi to RAMPS](http://beginner3dprinter.com/). The process would likely be very similar for your printer.

The biggest challenge will likely be setting up the firmware

BTW, what printer did you get?

> **Comments:**
> **username_0**: Fantastic answer! I ended up getting the Monoprice Maker Select v2.1 back in November. Couldn't beat the price and I saw it had a very large community of support. Made me really happy to see it's all parts that I've worked with and used before (Arduino and components).  
> **username_1**: I have a Tronxy X3.  My printer has Repetier Firmware.  I have found it on GitHub; but, that code base seems dormant.  Marlin Firmware has a very active Open Source development (https://github.com/MarlinFirmware).  I look forward to playing with the code and it looks like Marlin would be a better place to do that.  It appears that either firmware will run the printer well.  
> **username_0**: I like the simplicity of that design. No frills, no additional things to get in the way, just all that is needed to make it work. It looks like it has a rather large build space, too. I haven't seen too many people with a Tronxy--what do you think of it?  
> **username_1**: @username_0 I like the X3; but, it is my first printer so I don't have much to compare it to.  The one thing I can say for sure is that it would likely not be a good option for someone that doesn't like fiddling with things.  It does have a few issues; but, there is a strong maker community around it so there are are fixes for all the issues.  The reason I wanted is because I wanted to fiddle and the open design makes that easy to do.  I am very happy with the printer and have not had a print fail yet.  
> **username_2**: @username_1, Repetier is the firmware shipped with the Maker Select (Wanhao rebranded). Repetier is FAR from dormant, and, frankly, has better bed-leveling.  
> **username_1**: @username_2 Comparing the two firmwares on GitHub [Repetier](https://github.com/repetier/Repetier-Firmware) has 39 contributors and 999 commits (10 in the last 6mo) where [Marlin](https://github.com/MarlinFirmware/Marlin) has 415 contributors and 10,196 commits (437 in the last 6mo)  

---

