With the exception of the STX (X'02), ETX (X'03) and EM (X'19) control characters, the HSM expects all data to be encoded as either ASCII or EBCDIC characters. Where the HSM does not try and interpret the data (e.g., in the message header and message trailer fields), it is possible to include other control characters, but this is not good practice.
When sending data to the HSM, other than data that is already in character format, encode each digit (0-9, A-F) as a character (e.g., to send the hexadecimal value 1234ABCD to the HSM requires 8 characters).