Advantech ROM-5420 User Manual page 23

The 0x50 is the HDMI address. So you can try below command to know I2C bus is
work or not.
#i2cdump -f -y 1 0x50
No size specified (using byte-data access)
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: 00 ff ff ff ff ff ff 00 04 69 fd 22 03 01 01 01
10: 16 17 01 03 80 30 1b 78 2a 2a c5 a4 56 4f 9e 28
20: 0f 50 54 b7 ef 00 d1 c0 81 40 81 80 95 00 b3 00
30: 71 4f 81 c0 81 00 02 3a 80 18 71 38 2d 40 58 2c
40: 45 00 dc 0c 11 00 00 1e 00 00 00 ff 00 44 35 4c
50: 4d 51 53 30 39 36 30 34 38 0a 00 00 00 fd 00 32
60: 4b 18 53 11 00 0a 20 20 20 20 20 20 00 00 00 fc
70: 00 41 53 55 53 20 56 53 32 32 38 0a 20 20 01 f6
80: 02 03 22 71 4f 01 02 03 11 12 13 04 14 05 0e 0f
90: 1d 1e 1f 10 23 09 17 07 83 01 00 00 65 03 0c 00
a0: 10 00 8c 0a d0 8a 20 e0 2d 10 10 3e 96 00 dc 0c
b0: 11 00 00 18 01 1d 00 72 51 d0 1e 20 6e 28 55 00
c0: dc 0c 11 00 00 1e 01 1d 00 bc 52 d0 1e 20 b8 28
d0: 55 40 dc 0c 11 00 00 1e 8c 0a d0 90 20 40 31 20
e0: 0c 40 55 00 dc 0c 11 00 00 18 00 00 00 00 00 00
f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 b5
If there is nothing connected to HDMI port, the result should be as below:
#i2cdump -f -y 5 0x50
No size specified (using byte-data access)
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX
10: XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX
20: XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX
30: XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX
40: XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX
50: XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX
60: XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX
70: XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX
80: XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX
90: XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX
a0: XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX
b0: XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX
c0: XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX
d0: XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX
e0: XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX
f0: XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX
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15 ROM-5420 User Manual
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