I am using codesys v.2 and a slave device (LED Marquee display) that uses Modbus\tcp 984. The codesys function blocks for MB\tcp which were provided have an INT input for addresses of registers and doesn't allow me to enter in 6-digit addresses.

I have had a hard time finding documentation on the difference of 5 & 6 digit addressing, if anyone has experience in this or can help in any way it would be extremely appreciated.

 

They are not really 5 or 6 digit addresses. The addreses are 16 bit
integers 0-65535.

Most older PLCs only supported addresses from 0-999 or 0-9999.

New stuff supports addresses 0-65535.

In most cases, the first legal address (0) of each type of memory location are referred to as:
000001 - outputs/coils R/W
100001 - inputs R/O
300001 - input registers R/O
400001 - holding register R/W

In PLCs that only supported addresses 0-9999 these were shortened to
00001, 10001, 30001, 40001

They still used an INT for the address.