| 1.port + 0
2. port + 2
When read this port means clear the interrupt signal that generated from the adapter.
3.port + 6
4.port + 8
Counter 0 I/O buffer (8254 IC).
5.port + 9
Counter 1 I/O buffer (8254 IC).
6.port + A
Counter 2 I/O buffer (8254 IC).
7.port + B
Counter control register (8254 IC).
port address+0 is used to control A/D conversion. The low 8 bit control
format is :|
1.Select A/D channel number
The C0 to C3 are used to select input channel number.
The R0 to R2 are used to select gain control factor, if JP1 is short, the R0 to R2 are disable.
3.Sampling and hold
The “x” bit is used to control sampling and hold, when write 0 to this bit, it latch the input voltage to let A/D converter get the input voltage, otherwise when write 1 to this bit, it enter sampling mode. Normally, this bit is 1.
4.Select trig method
The SE0 and SE1 are used to select trig method for A/D converter, user can select software trig, external hardware trig or trig by 8254.
ENX is used to enable/disable external hardware trig, when this bit is set to 0, it means disable external trig, otherwise this bit is set to 1 means enable external trig. When user select external hardware trig, he must connect external signal to J1 pin 2. When 8254 trig is selected, this bit must be set to 1.