how do i not update the bootloader?
L.E. never mind, i found how to update the bootloader.
i'm not going to do that.

how do i not update the bootloader?
L.E. never mind, i found how to update the bootloader.
i'm not going to do that.

the new 3hc board arrived, it was replaced on warranty and it communicates, the leds blink at the same time and i can talk to it. it has 3.1.0 firmware on it and i have to admit i'm afraid of upgrading it to the last firmware. anything i should be careful about?

ok, thank you

@dc42 help

ok, so i followed your steps and here are the results:

1. 6HC has firmware 3.1.1 with no 3hc update file on its sd card. no can cable connected but both boards powered on, the 3HC blinks 4 times and another brief one.
2. i connected the CAN cable, 3HC led still flashes 4 times. all address pins set to 0. i reset the 3HC, the led still flashes 4 times. nothing changed.

if i install firmware 3.2.2 on 6HC:

1. 6HC has firmware 3.2.2 with no 3hc update file on it's sd card. no can cable connected but both boards powered on, the 3HC blinks 4 times and another brief one.
2. i connected the CAN cable, the led blinks 5 times, YAT reports
   Error: Received firmware update request for missing file 'Duet3Firmware_EXP3HC.bin'
3. i placed Duet3Firmware_EXP3HC.bin from firmware 3.1.1 on the sd card, mounted the sd card, the led from the 3HC stops flashing all toghether. if i send M115 B126 -
   Error: M115: Response timeout: CAN addr 126, req type 6024, RID=0
   if i remove the CAN cable the 3HC starts flashing 4 times. i remove the 3hc update file from the sd card, the 3hc led starts flashing 5 times - yat reports Error: Received firmware update request for missing file 'Duet3Firmware_EXP3HC.bin'
   i upload the Duet3Firmware_EXP3HC.bin from 3.2.2 and mount the sd card
   the led stops flashing.
   sending m115 b126 gives:
   Error: M115: Response timeout: CAN addr 126, req type 6024, RID=1
   after reset same response.
   switch to address 1: same response, different address

Thanx a lot, I'll try that tomorrow and get back with results.

So? Is the 6hc broke or the 3hc?

Do I need to tell the mainboard anywhere that there is an explanation board attached? In a config file?

@jay_s_uk m997 b1
Error: M997: Response timeout: CAN addr 1, req type 6024, RID=3

so the result from M122 is:
m122
=== Diagnostics ===
RepRapFirmware for Duet 3 MB6HC version 3.2.2 running on Duet 3 MB6HC v1.01 or later (standalone mode)
Board ID: 08DJM-956BA-NA3TJ-6JKDD-3S06T-KU82T
Used output buffers: 1 of 40 (1 max)
=== RTOS ===
Static ram: 149788
Dynamic ram: 91308 of which 604 recycled
Never used RAM 117132, free system stack 185 words
Tasks: NETWORK(ready,545) HEAT(blocked,368) CanReceiv(blocked,927) CanSender(blocked,371) CanClock(blocked,356) TMC(blocked,60) MAIN(running,1325) IDLE(ready,19)
Owned mutexes: USB(MAIN)
=== Platform ===
Last reset 00:00:23 ago, cause: reset button
Last software reset at 2021-02-21 15:52, reason: User, GCodes spinning, available RAM 110284, slot 2
Software reset code 0x0003 HFSR 0x00000000 CFSR 0x00000000 ICSR 0x0044a000 BFAR 0x00000000 SP 0x00000000 Task MAIN Freestk 0 n/a
Error status: 0x00
Aux0 errors 0,0,0
Aux1 errors 0,0,0
MCU temperature: min 39.3, current 40.9, max 41.1
Supply voltage: min 25.4, current 25.6, max 26.2, under voltage events: 0, over voltage events: 0, power good: yes
12V rail voltage: min 12.1, current 12.1, max 12.2, under voltage events: 0
Driver 0: position 0, standstill, reads 740, writes 11 timeouts 0, SG min/max 0/0
Driver 1: position 0, standstill, reads 740, writes 11 timeouts 0, SG min/max 0/0
Driver 2: position 0, standstill, reads 740, writes 11 timeouts 0, SG min/max 0/0
Driver 3: position 0, standstill, reads 740, writes 11 timeouts 0, SG min/max 0/0
Driver 4: position 0, standstill, reads 740, writes 11 timeouts 0, SG min/max 0/0
Driver 5: position 0, standstill, reads 741, writes 11 timeouts 0, SG min/max 0/0
Date/time: 1970-01-01 00:00:00
Slowest loop: 999.15ms; fastest: 0.05ms
=== Storage ===
Free file entries: 10
SD card 0 detected, interface speed: 25.0MBytes/sec
SD card longest read time 2.2ms, write time 0.0ms, max retries 0
=== Move ===
DMs created 125, maxWait 0ms, bed compensation in use: none, comp offset 0.000
=== MainDDARing ===
Scheduled moves 0, completed moves 0, hiccups 0, stepErrors 0, LaErrors 0, Underruns [0, 0, 0], CDDA state -1
=== AuxDDARing ===
Scheduled moves 0, completed moves 0, hiccups 0, stepErrors 0, LaErrors 0, Underruns [0, 0, 0], CDDA state -1
=== Heat ===
Bed heaters = -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1, chamberHeaters = -1 -1 -1 -1
=== GCodes ===
Segments left: 0
Movement lock held by null
HTTP is idle in state(s) 0
Telnet is idle in state(s) 0
File is idle in state(s) 0
USB is ready with "m122" in state(s) 0
Aux is idle in state(s) 0
Trigger is idle in state(s) 0
Queue is idle in state(s) 0
LCD is idle in state(s) 0
SBC is idle in state(s) 0
Daemon is idle in state(s) 0
Aux2 is idle in state(s) 0
Autopause is idle in state(s) 0
Code queue is empty.
=== Network ===
Slowest loop: 0.15ms; fastest: 0.00ms
Responder states: HTTP(0) HTTP(0) HTTP(0) HTTP(0) HTTP(0) HTTP(0) FTP(0) Telnet(0), 0 sessions Telnet(0), 0 sessions
HTTP sessions: 0 of 8

• Ethernet -
  State: disabled
  Error counts: 0 0 0 0 0
  Socket states: 0 0 0 0 0 0 0 0
  === CAN ===
  Messages queued 1, send timeouts 0, received 0, lost 0, longest wait 0ms for reply type 0, free buffers 48
  ok

i did receive earlier this message:
=== CAN ===
Messages queued 5863, send timeouts 55, received 5, lost 0, longest wait 0ms for reply type 0, free buffers 48
where it says it received 5 messages from the expansion board.

i receive this:
m115 b1
Error: M115: Response timeout: CAN addr 1, req type 6024, RID=1
ok

but if i send:
m997 s1
ok

it says ok as if it managed to install the firmware on expansion board 1?