diff --git a/src/doc/avrdude.texi b/src/doc/avrdude.texi
index d6009d3c..c45f7e26 100644
--- a/src/doc/avrdude.texi
+++ b/src/doc/avrdude.texi
@@ -307,6 +307,13 @@ The MPLAB(R) PICkit 4, MPLAB(R) SNAP, and Curiosity Nano boards are
supported in UPDI mode. The Curiosity Nano board is dubbed ``PICkit on
Board'', thus the name @code{pkobn_updi}.
+SerialUPDI programmer implementation is based on Microchip's
+@emph{pymcuprog} (@url{https://github.com/microchip-pic-avr-tools/pymcuprog})
+utility, but it also contains some performance improvements included in
+Spence Kohde's @emph{DxCore} Arduino core (@url{https://github.com/SpenceKonde/DxCore}).
+In a nutshell, this programmer consists of simple USB->UART adapter, diode
+and couple of resistors. It uses serial connection to provide UPDI interface.
+@xref{SerialUPDI programmer} for more details and known issues.
@menu
* History::
@@ -1773,6 +1780,7 @@ functionality does not make sense for these boot loaders.
@menu
* Atmel STK600::
* Atmel DFU bootloader using FLIP version 1::
+* SerialUPDI programmer::
@end menu
@c
@@ -1874,7 +1882,7 @@ least 4.5 V in order to work. This can be done using
@c
@c Node
@c
-@node Atmel DFU bootloader using FLIP version 1, , Atmel STK600, Programmer Specific Information
+@node Atmel DFU bootloader using FLIP version 1, SerialUPDI programmer , Atmel STK600, Programmer Specific Information
@section Atmel DFU bootloader using FLIP version 1
Bootloaders using the FLIP protocol version 1 experience some very
@@ -1899,6 +1907,109 @@ signature check to be overridden with the @option{-F} option.
A @emph{chip erase} might leave the EEPROM unerased, at least on some
versions of the bootloader.
+@c
+@c Node
+@c
+@node SerialUPDI programmer, , Atmel DFU bootloader using FLIP version 1, Programmer Specific Information
+@section SerialUPDI programmer
+
+SerialUPDI programmer can be used for programming UPDI-only devices
+using very simple serial connection.
+You can read more about the details here
+@url{https://github.com/SpenceKonde/AVR-Guidance/blob/master/UPDI/jtag2updi.md}
+
+SerialUPDI programmer has been tested using FT232RL USB->UART interface
+with the following connection layout (copied from Spence Kohde's page linked
+above):
+
+@example
+-------------------- To Target device
+ DTR| __________________
+ Rx |--------------,------------------| UPDI---\/\/---------->
+ Tx---/\/\/\---Tx |-------|<|---' .--------| Gnd 470 ohm
+ resistor Vcc|---------------------------------| Vcc
+ 1k CTS| .` |__________________
+ Gnd|--------------------'
+--------------------
+@end example
+
+There are several limitations in current SerialUPDI/AVRDUDE integration,
+listed below.
+
+At the end of each run there are fuse values being presented to the user.
+For most of the UPDI-enabled devices these definitions (low fuse, high
+fuse, extended fuse) have no meaning whatsoever, as they have been
+simply replaced by array of fuses: fuse0..9. Therefore you can simply
+ignore this particular line of AVRDUDE output.
+
+In connection to the above, @emph{safemode} has no meaning in context
+of UPDI devices and should be ignored.
+
+Currently available devices support only UPDI NVM programming model 0
+and 2, but there is also experimental implementation of model 3 - not
+yet tested.
+
+One of the core AVRDUDE features is verification of the connection by
+reading device signature prior to any operation, but this operation
+is not possible on UPDI locked devices. Therefore, to be able to
+connect to such a device, you have to provide @option{-F} to override
+this check.
+
+Please note: using @option{-F} during write operation to locked device
+will force chip erase. Use carefully.
+
+Another issue you might notice is slow performance of EEPROM writing
+using SerialUPDI for AVR Dx devices. This can be addressed by changing
+@emph{avrdude.conf} section for this device - changing EEPROM page
+size to 0x20 (instead of default 1), like so:
+
+@example
+#------------------------------------------------------------
+# AVR128DB28
+#------------------------------------------------------------
+
+part parent ".avrdx"
+ id = "avr128db28";
+ desc = "AVR128DB28";
+ signature = 0x1E 0x97 0x0E;
+
+ memory "flash"
+ size = 0x20000;
+ offset = 0x800000;
+ page_size = 0x200;
+ readsize = 0x100;
+ ;
+
+ memory "eeprom"
+ size = 0x200;
+ offset = 0x1400;
+ page_size = 0x1;
+ readsize = 0x100;
+ ;
+;
+@end example
+
+USERROW memory has not been defined for new devices except for
+experimental addition for AVR128DB28. The point of USERROW is to
+provide ability to write configuration details to already locked
+device and currently SerialUPDI interface supports this feature,
+but it hasn't been tested on wide variety of chips. Treat this as
+something experimental at this point. Please note: on locked devices
+it's not possible to read back USERROW contents when written, so
+the automatic verification will most likely fail and to prevent
+error messages, use @option{-V}.
+
+Please note that SerialUPDI interface is pretty new and some
+issues are to be expected. In case you run into them, please
+make sure to run the intended command with debug output enabled
+(@option{-v -v -v}) and provide this verbose output with your
+bug report. You can also try to perform the same action using
+@emph{pymcuprog} (@url{https://github.com/microchip-pic-avr-tools/pymcuprog})
+utility with @option{-v debug} and provide its output too.
+You will notice that both outputs are pretty similar, and this
+was implemented like that on purpose - it was supposed to make
+analysis of UPDI protocol quirks easier.
+
@c
@c Node
@c