# Copy HEX from Uno to Nano issue **URL:** \ **Category:** Programming\ **Created:** [July 20, 2025, 1:10am UTC](https://forum.arduino.cc/t/copy-hex-from-uno-to-nano-issue/1396723 "2025-07-20T01:10:38Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![chaos0711](https://avatars.discourse-cdn.com/v4/letter/c/5fc32e/32.png) [@chaos0711](https://forum.arduino.cc/u/chaos0711)\ **Post date:** [July 20, 2025, 1:10am UTC](https://forum.arduino.cc/t/copy-hex-from-uno-to-nano-issue/1396723/1 "2025-07-20T01:10:38Z")
Trying to get a copy of GRBL to run on a Nano clone with a 3drive shield. Have an Uno running correctly and have used AVRDude to copy the flash image to a file. Nano will compile and program, but nothing comes out of the serial port. Have tried direct USB connection and RX/TX to FT1232 board. Have confirmed that the Nano will output serial both ways as well. Nano bootloader has been set as an Uno, otherwise the image is too big to fit. Both are using the 328P MCU. Serial chip on nano is a CH340, but that should really only matter to the PC I'm connecting it to. Nano works for everything else, just not this. Also tried to copy the Uno hex file directly into the Nano using AVRDude. After the hex copy, dumped the Nano flash back to separate file and compared. Found differences. Why? Working Uno flash file has data in the 0x7800-0x7AC0 range while the Nano dump has all FF's in this range. This section is the only piece that is different. What is it? Why would it prevent the Nano from talking on the serial? Why didn't it copy over from the Uno hex file? ```arduino 20780000739FB00DA11D621F839FA00D611D221F749F3327A00D611D231F849F600D211D24 :20782000822F762F6A2F11249F5750409AF0F1F088234AF0EE0FFF1FBB1F661F771F881F97 :2078400091505040A9F79E3F510580F00C94983A0C948A3B5F3FE4F3983ED4F38695779564 :207860006795B795F795E7959F5FC1F7FE2B880F911D9695879597F908950E94573BE8F014 :207880009E37E8F09639B8F49E3848F4672F782F8827985FF9CF86957795679593959539EA :2078A000D0F3B62FB1706B0F711D811D20F487957795679593950C949E3A0C94B93A0C944E :2078C0008A3B9F930E94013B0F9007FCEE5F0C943B3B19F416F40C94C73A0C94B93A0E94E1 :2078E000573BB8F39923C9F3B6F39F57550B87FF0E94BE3C0024A0E640EA9001805856958A :20790000979528F4805C660F771F881F20F026173707480730F4621B730B840B2029312966 :207920004A2BA69517940794202531254A2758F7660F771F881F20F026173707480730F446 :20794000620B730B840B200D311D411DA09581F7B901842F9158880F9695879508959B01BA :20796000AC010C94D03B0E94713B30F09F3710F40C948A3B0C949E3A0C94B93A9150504086 :20798000660F771F881FD2F708959F938F937F936F93FF93EF939B01AC010E94D03BEF91DD :2079A000FF910E94CA3A2F913F914F915F910C94D03B991B79E004C0991F961708F0961BA7 :2079C000881F7A95C9F780950895AA1BBB1B51E107C0AA1FBB1FA617B70710F0A61BB70B4A :2079E000881F991F5A95A9F780959095BC01CD010895A1E21A2EAA1BBB1BFD010DC0AA1F3D :207A0000BB1FEE1FFF1FA217B307E407F50720F0A21BB30BE40BF50B661F771F881F991F13 :207A20001A9469F760957095809590959B01AC01BD01CF010895052E97FB1EF400940E9483 :207A4000323D57FD07D00E94F93C07FC03D04EF40C94323D50954095309521953F4F4F4F2D :207A60005F4F089590958095709561957F4F8F4F9F4F0895EE0FFF1F0590F491E02D099470 :207A80000E944B3DA59F900DB49F900DA49F800D911D11240895A29FB001B39FC001A39F54 :207AA000700D811D1124911DB29F700D811D1124911D0895FB01DC0104C08D9101908019F7 :207AC00021F441505040C8F7881B990B0895F894FFCFFFFFFFFFFFFFFFFFFFFFFFFFFFFF81 ``` ---
**Author:** ![david\_2018](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/david_2018/32/1013044_2.png) [@david\_2018](https://forum.arduino.cc/u/david_2018)\ **Post date:** [July 20, 2025, 3:15am UTC](https://forum.arduino.cc/t/copy-hex-from-uno-to-nano-issue/1396723/2 "2025-07-20T03:15:46Z")
> [@chaos0711](#): > > Nano bootloader has been set as an Uno, otherwise the image is too big to fit. Did you actually burn the UNO bootloader to the Nano? ---
**Author:** ![Grumpy\_Mike](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/grumpy_mike/32/213521_2.png) [@Grumpy\_Mike](https://forum.arduino.cc/u/Grumpy_Mike)\ **Post date:** [July 20, 2025, 5:27am UTC](https://forum.arduino.cc/t/copy-hex-from-uno-to-nano-issue/1396723/3 "2025-07-20T05:27:48Z")
Seeing as the Uno and Nano Classic use exactly the same processor, then there is no reason why it should not fit. ---
**Author:** ![chaos0711](https://avatars.discourse-cdn.com/v4/letter/c/5fc32e/32.png) [@chaos0711](https://forum.arduino.cc/u/chaos0711)\ **Post date:** [July 20, 2025, 5:44am UTC](https://forum.arduino.cc/t/copy-hex-from-uno-to-nano-issue/1396723/4 "2025-07-20T05:44:48Z")
Arduino IDE will not take the GRBL code if the device is set as a Nano - with either of the bootloaders. Google search said something about old ROM code that they didn't want to fix, and just burn as an Uno. ---
**Author:** ![Grumpy\_Mike](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/grumpy_mike/32/213521_2.png) [@Grumpy\_Mike](https://forum.arduino.cc/u/Grumpy_Mike)\ **Post date:** [July 20, 2025, 5:47am UTC](https://forum.arduino.cc/t/copy-hex-from-uno-to-nano-issue/1396723/5 "2025-07-20T05:47:34Z")
> [@chaos0711](#): > > Google search said something about old ROM code that they didn't want to fix, and just burn as an Uno. I think you misunderstood what you were being told here. On the other hand it cold just be rubbish. Can you post the link to where you got that from please. ---
**Author:** ![chaos0711](https://avatars.discourse-cdn.com/v4/letter/c/5fc32e/32.png) [@chaos0711](https://forum.arduino.cc/u/chaos0711)\ **Post date:** [July 20, 2025, 5:47am UTC](https://forum.arduino.cc/t/copy-hex-from-uno-to-nano-issue/1396723/6 "2025-07-20T05:47:47Z")
@david_2018 Reasonably sure I did. Set up 4 of these and did a bootload burn on all 4. Pretty sure I set it as Uno... I suppose I can always got back and do it again just to be sure. Still doesn't explain why the HEX write was different. Made sure to have AVRDude erase first and it still has that separate section. ---
**Author:** ![chaos0711](https://avatars.discourse-cdn.com/v4/letter/c/5fc32e/32.png) [@chaos0711](https://forum.arduino.cc/u/chaos0711)\ **Post date:** [July 20, 2025, 5:50am UTC](https://forum.arduino.cc/t/copy-hex-from-uno-to-nano-issue/1396723/7 "2025-07-20T05:50:25Z")
> [@Nano vs uno: max sketch size differences, why?](https://forum.arduino.cc/t/nano-vs-uno-max-sketch-size-differences-why/901931): > > Why the max sketch size in a nano is 30720bytes and in uno is 32256 bytes???? It´s supposed to be the same microcontroller, ATmega328P, I don´t understand. \*\*\* It´s possible to get max sketch size of 32256 bytes in a nano? How? Thanks in advance!! I may have misspoken the context.. but the result is the same. Nano has a different bootloader than Uno, even though the chips are the same. ---
**Author:** ![chaos0711](https://avatars.discourse-cdn.com/v4/letter/c/5fc32e/32.png) [@chaos0711](https://forum.arduino.cc/u/chaos0711)\ **Post date:** [July 20, 2025, 5:54am UTC](https://forum.arduino.cc/t/copy-hex-from-uno-to-nano-issue/1396723/8 "2025-07-20T05:54:36Z")
.... and now the Uno is throwing an error code. FML... it was working. _grumble_ Separate issue though. Not gonna bring it up here, just need to pull it back out _again_ and rewrite. Sometimes, DIY is a real PITA. 🙂 ---
**Author:** ![Grumpy\_Mike](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/grumpy_mike/32/213521_2.png) [@Grumpy\_Mike](https://forum.arduino.cc/u/Grumpy_Mike)\ **Post date:** [July 20, 2025, 6:01am UTC](https://forum.arduino.cc/t/copy-hex-from-uno-to-nano-issue/1396723/9 "2025-07-20T06:01:55Z")
Look at these official data sheets [Nano](https://docs.arduino.cc/hardware/nano/) [Uno R3](https://docs.arduino.cc/hardware/uno-rev3/) Look at them and tell me where you see there are 1536 more bytes of flash memory in the Nano than the Uno. They are the same chip! They both have 32K of flash memory. ---
**Author:** ![chaos0711](https://avatars.discourse-cdn.com/v4/letter/c/5fc32e/32.png) [@chaos0711](https://forum.arduino.cc/u/chaos0711)\ **Post date:** [July 20, 2025, 6:09am UTC](https://forum.arduino.cc/t/copy-hex-from-uno-to-nano-issue/1396723/10 "2025-07-20T06:09:49Z")
@Grumpy_Mike I know this.. and you know this. Arduino IDE does not know this. Go download the GRBL code and see for yourself. It compiles to 31346 bytes, which is 97% of the Uno memory. If you try to burn that while set as a Nano, it says 102% and will not write. ---
**Author:** ![Grumpy\_Mike](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/grumpy_mike/32/213521_2.png) [@Grumpy\_Mike](https://forum.arduino.cc/u/Grumpy_Mike)\ **Post date:** [July 20, 2025, 6:13am UTC](https://forum.arduino.cc/t/copy-hex-from-uno-to-nano-issue/1396723/11 "2025-07-20T06:13:11Z")
> [@chaos0711](#): > > Go download the GRBL code Got a link to that? ---
**Author:** ![chaos0711](https://avatars.discourse-cdn.com/v4/letter/c/5fc32e/32.png) [@chaos0711](https://forum.arduino.cc/u/chaos0711)\ **Post date:** [July 20, 2025, 6:19am UTC](https://forum.arduino.cc/t/copy-hex-from-uno-to-nano-issue/1396723/12 "2025-07-20T06:19:25Z")
@Grumpy_Mike > **[GitHub - gnea/grbl: An open source, embedded, high performance...](https://github.com/gnea/grbl)** > > An open source, embedded, high performance g-code-parser and CNC milling controller written in optimized C that will run on a straight Arduino ---
**Author:** ![Grumpy\_Mike](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/grumpy_mike/32/213521_2.png) [@Grumpy\_Mike](https://forum.arduino.cc/u/Grumpy_Mike)\ **Post date:** [July 20, 2025, 6:31am UTC](https://forum.arduino.cc/t/copy-hex-from-uno-to-nano-issue/1396723/13 "2025-07-20T06:31:11Z")
Downloaded it but it just consists of rubbish and therefore will not compile as anything. ```arduino config.h coolant_control.c coolant_control.h cpu_map.h defaults.h eeprom.c eeprom.h examples gcode.c gcode.h grbl.h jog.c jog.h limits.c limits.h main.c motion_control.c motion_control.h nuts_bolts.c nuts_bolts.h planner.c planner.h print.c print.h probe.c probe.h protocol.c protocol.h report.c report.h serial.c serial.h settings.c settings.h spindle_control.c spindle_control.h stepper.c stepper.h system.c system.h ``` ---
**Author:** ![chaos0711](https://avatars.discourse-cdn.com/v4/letter/c/5fc32e/32.png) [@chaos0711](https://forum.arduino.cc/u/chaos0711)\ **Post date:** [July 20, 2025, 6:34am UTC](https://forum.arduino.cc/t/copy-hex-from-uno-to-nano-issue/1396723/14 "2025-07-20T06:34:37Z")
@Grumpy_Mike In the examples directory is the INO file. Load that and compile. Don't edit anything. ---
**Author:** ![Grumpy\_Mike](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/grumpy_mike/32/213521_2.png) [@Grumpy\_Mike](https://forum.arduino.cc/u/Grumpy_Mike)\ **Post date:** [July 20, 2025, 6:42am UTC](https://forum.arduino.cc/t/copy-hex-from-uno-to-nano-issue/1396723/15 "2025-07-20T06:42:16Z")
And I get on verification > Arduino: 1.8.19 (Mac OS X), B > Alternatives for grbl.h: [] > grblUpload:27:10: fatal error: grbl.h: No such file or directoryResolveLibrary(grbl.h) > > -\> candidates: [] #include \ > > ``` > ^ ~~~~~~~ > > ``` > > compilation terminated. > exit status 1 > grbl.h: No such file or directory ---
**Author:** ![chaos0711](https://avatars.discourse-cdn.com/v4/letter/c/5fc32e/32.png) [@chaos0711](https://forum.arduino.cc/u/chaos0711)\ **Post date:** [July 20, 2025, 6:55am UTC](https://forum.arduino.cc/t/copy-hex-from-uno-to-nano-issue/1396723/16 "2025-07-20T06:55:08Z")
@Grumpy_Mike You put the entire GRBL directory in the Arduino library directory. Open the INO file in the grbl/examples and compile/upload. I promise you, it is a valid sketch and it all works properly. and that if you have the IDE set for NANO, it will not upload. But if you have it set for Uno, it will. ---
**Author:** ![westfw](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/westfw/32/213443_2.png) [@westfw](https://forum.arduino.cc/u/westfw)\ **Post date:** [July 20, 2025, 8:55am UTC](https://forum.arduino.cc/t/copy-hex-from-uno-to-nano-issue/1396723/17 "2025-07-20T08:55:56Z")
> [@Grumpy\_Mike](#): > > tell me where you see there are 1536 more bytes of flash memory in the Nano than the Uno. The nano has the bootloader size set to 2k, even if it has the “new” 512byte optiboot bootloader. Thus, it has LESS usable flash…. ---
**Author:** ![jim-p](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/jim-p/32/922840_2.png) [@jim-p](https://forum.arduino.cc/u/jim-p)\ **Post date:** [July 20, 2025, 9:33am UTC](https://forum.arduino.cc/t/copy-hex-from-uno-to-nano-issue/1396723/18 "2025-07-20T09:33:52Z")
> [@chaos0711](#): > > It compiles to 31346 bytes, which is 97% of the Uno memory. > If you try to burn that while set as a Nano, it says 102% and will not write. That is because the upload.maximum\_size for the Nano is set to 30720 but for the Uno it is 32265. You can modify the boards.txt file and change it to 32265 for the Nano, then it should work. FYI: The regular bootloader for the Uno and Nano are the same. ---
**Author:** ![cedarlakeinstruments](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/cedarlakeinstruments/32/1128931_2.png) [@cedarlakeinstruments](https://forum.arduino.cc/u/cedarlakeinstruments)\ **Post date:** [July 20, 2025, 11:13am UTC](https://forum.arduino.cc/t/copy-hex-from-uno-to-nano-issue/1396723/19 "2025-07-20T11:13:56Z")
I have grbl running on two nanos although ISTR that they both are from a batch than needs the "old bootloader" selected in the IDE. I do not recall having to do anything special to get them to work. ---
**Author:** ![david\_2018](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/david_2018/32/1013044_2.png) [@david\_2018](https://forum.arduino.cc/u/david_2018)\ **Post date:** [July 20, 2025, 12:15pm UTC](https://forum.arduino.cc/t/copy-hex-from-uno-to-nano-issue/1396723/20 "2025-07-20T12:15:10Z")
> [@jim-p](#): > > You can modify the boards.txt file and change it to 32265 for the Nano, then it should work. > > FYI: The regular bootloader for the Uno and Nano are the same. Or do as @chaos0711, and many others, have done and burn the bootloader to the Nano with the board selection set to UNO. Just have to remember to always select UNO as the board type when compiling for that Nano. [Next page](https://forum.arduino.cc/t/copy-hex-from-uno-to-nano-issue/1396723.md?page=2)