# Loading Firmware Changes the RS-232 Speed

Firmware is always sent at 38,400 bits per second (bit/s).

The KX3 Utility determines the KX3's initial RS-232 speed by analyzing responses to short "no operation" commands (;) sent at various speeds. The KX3 Utility then changes the KX3 to 38,400 bit/s to send firmware. After firmware is sent, the KX3 Utility attempts to change the KX3's RS-232 speed back to the original value.

If the operation is interrupted or communications cannot be established with the KX3's MCU after sending firmware, the KX3 Utility cannot restore the RS-232 speed to its original value. After restart, the you may find the RS-232 speed set to 38,400 bit/s.

The KX3 commands used to change RS-232 speed require interaction with operational MCU firmware. A KX3 in its "boot loader" state, indicated by a KX3 display showing "MCU LD" and a red Tx light, communicates only at 38,400 bit/s. Once MCU firmware is loaded, the speed last used by the most recently-loaded MCU firmware is discovered (by polling at all the KX3's supported speeds) and that's where it is left after firmware load is complete.

RS-232 speed changes are displayed in the Activity Log.

If the KX3's RS-232 speed needs to be changed, use the KX3 CONFIG:RS-232 menu selection.

You may also use the Command Tester to enter a KX3 "br" command to change the KX3's RS-232 speed:

- "br0;" sets the KX3 to 4800 bit/s
- "br1;" sets it to 9600 bit/s
- "br2;" sets it to 19,200 bit/s
- "br3;" sets it to 38,400 bit/s

The Elecraft K3 and KX3 Programmer's Reference provides KX3 command information.

After you change the RS-232 speed with the KX3 CONFIG:RS-232 menu or the Command Tester, use the Test Communications button to allow the KX3 Utility to discover the KX3's current RS-232 speed.