Granted the error was on my side... (I had my bits and bytes incorrect)
However the ECOMM100 maybe should have responded with something.
Firmware 4.0.269
Booter 4.0.165
From Wireshark:
No. Time Source Destination Protocol Info
664 33.178201 192.168.1.109 192.168.1.100 Modbus/TCP query [ 1 pkt(s)]: trans: 1; unit: 255, func: 15: Force Multiple Coils.
Frame 664: 69 bytes on wire (552 bits), 69 bytes captured (552 bits)
Ethernet II, Src: Intel_4f:a6:32 (00:07:e9:4f:a6:32), Dst: HostEngi_20:e9:db (00:e0:62:20:e9:db)
Internet Protocol, Src: 192.168.1.109 (192.168.1.109), Dst: 192.168.1.100 (192.168.1.100)
Transmission Control Protocol, Src Port: xinuexpansion4 (2024), Dst Port: asa-appl-proto (502), Seq: 1, Ack: 1, Len: 15
Modbus/TCP
transaction identifier: 1
protocol identifier: 0
length: 9
unit identifier: 255
Modbus
function 15: Force Multiple Coils
reference number: 3104
bit count: 24
byte count: 2
Data
0000 00 e0 62 20 e9 db 00 07 e9 4f a6 32 08 00 45 00 ..b .....O.2..E.
0010 00 37 79 2e 40 00 80 06 fd 70 c0 a8 01 6d c0 a8 .7y.@....p...m..
0020 01 64 07 e8 01 f6 b6 ec 79 21 1d ec c0 a2 50 18 .d......y!....P.
0030 ff ff 05 cf 00 00 00 01 00 00 00 09 ff 0f 0c 20 ...............
0040 00 18 02 00 00 .....