4.3.4 Interrupt Source Control
In ISC register (offset 0x20), there are four bits to control the IRQ sources of INT1 and INT2.
If the application need only one IRQ, you can disable one of the IRQ sources by software. If your application doesn't need any IRQ source, you
can disable both interrupts. However, the PCI BIOS still assigns an IRQ level to the PCI card and occupies the PC resource if you only disable the IRQ sources without changing the i nitial condition of the PCI controller.
It is not recommended to change the initial condition of the PCI card through
a user's own application software. If users want to disable the IRQ level, they can use the utility "util DIO 48H.exe" or "util DIO 96H.exe to change
the power on an interrupt setting.
The table 4.3 shows the register format of the ISC (address offset 0x20). This register is write only. The 4 LSBs are used to control the source of INT1 and INT2.
INT1 | D3 | D2 | D1 | D0 | IRQ Sources | IRQ Trigger Condition |
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|
|
|
|
|
|
Disable | X | X | 0 | 0 | INT1 disable | |
Mode 1 | X | X | 0 | 1 | ~P1C0 | falling edge of P1C0 |
Mode 2 | X | X | 1 | 0 | P1C0 OR ~P1C3 | (see following) |
Mode 3 | X | X | 1 | 1 | Event Counter | Counter count down to 0 |
INT2 | D3 | D2 | D1 | D0 | IRQ Sources | IRQ Trigger Condition |
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|
|
|
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|
|
Disable | 0 | 0 | X | X | INT2 disable | |
Mode 1 | 0 | 1 | X | X | ~P2C0 | falling edge of P2C0(*) |
Mode 2 | 1 | 0 | X | X | P2C0 OR ~P2C3 | (see following) (*) |
Mode 3 | 1 | 1 | X | X | Timer Output | Timer count down to 0 |
Table 4.3 ISC register format
(*) Note: Not available on PCIDIO 24H.
Then the IRQ | sources | is set as “P1C0 OR ~P1C3”, the IRQ trigger | |||
conditions are summarized in table 4.4. | |||||
|
|
|
|
|
|
| P1/2C0 | P1/2C3 |
| IRQ Trigger Condition |
|
| High | X |
| PC0=‘H’ disable all IRQ |
|
| X | Low |
| PC3=‘L’ disable all IRQ |
|
| Low |
| PC3 falling edge trigger when PC0=L |
| |
| High |
| PC0 rising edge trigger when PC3=H |
| |
Table 4.4 IRQ Trigger conditions
Because the P1/P2C0 and P1/P2C3 are external signals, the users can utilize the combination of the four signals to generate a proper IRQ.