FOUR PORT RS-232 SERIAL INTERFACE
4.2 Interrupt-Mode Options
Jumper E5 selects the interrupt mode for each port. Each port must be set in the correct mode to ensure proper installation.
“N” indicates the normal, single interrupt per port mode (Figure 4-2). “S” indicates the shared interrupt mode, which allows more than one port to access a single IRQ (Figure 4-4). “M” indicates the inclusion of a 1K ohm pull-down resistor required on one port when sharing interrupts (Figure 4-3).
1 2
M
S
N
M
S
N
3 4
Figure 4-2. E5 in normal mode.
Set jumpers to “S” for shared interrupt mode on all blocks sharing an IRQ except one. Set that port block for “M.” This provides the pull-down resistor circuit that makes sharing of IRQs possible. If you are using more than one Four Port RS-232 Serial Interface or a compatible card in a bus, you should have only one port set to “M.” Figure 4-3 shows all four ports sharing a single IRQ.
1 2
M
S
N
M
S
N
3 4
Figure 4-3. E5, sharing a single IRQ.
