*note by 1net: Please take the above description with a grain of salt as it is NOT for 7004. In upd7004, we have only 2 registers: 4000 and 4001. The upd7004 has only 10bit mode, but since the code only reads 4001, the resolution is effectively 8bit... the 2lsb are discarded and not read.

• the external interrupt 1 routine jumpes to 006Ch, where it reads the value from 4001h (A/D low byte).

• the external interrupt 1 routine jumpes to 0064h, where it reads the value from 4001h (A/D HIGH byte).