The Output Control Register, Input Control Register and Input Size Register are populated from the lower bits of the characters in the format string, streamlining the parsing procedure:

1. Upon parsing a Field Header, set Output Control Register Bit 13
2. A packing directive may immediately follow and set Input Control Register Bit 7
3. In general, the Output Control and Input Control registers are set by the lower bits of the character data in the format field string.
4. The Flag characters each correspond to a single bit in the Output Control Register.
5. Output Control Register Bits 2, 5, 8 toggle to 1 if a corresponding Selector character appears in the conversion specifier. They are 0 otherwise.
6. A final Input Size sets the lower 4 bits of the Input Size Register.