The port controllers (excepting FPC1) have a 32 byte PROM. This is used to give each port controller a unique Id. The PROM is connected on IO select line 5, and provides data on the top 8 bits of the data bus. The format of the data is given in table 8.
The PROM used has unprogrammed value of zeros, so reserved and unused fields should be set to zero. The flag bits indicate what is in this PROM, as shown in table 9.
Table 9: Id flag byte data format
