RS-422/485 SERIAL INTERFACE PLUS, 4-PORT
2.4.2MODEM CONTROL SIGNALS
Some software packages require the use of modem handshake signals such as CTS or DCD. Refer to your application software manual to determine the requirements for modem control signals. If no requirements are mentioned, a safe configuration is to tie DTR to DSR and DCD, and tie RTS to CTS. This configuration will typically satisfy the modem
2.4.3INTERRUPTS
A good analogy of a PC interrupt would be a phone ringing. The phone “bell” is a request for us to stop what we are currently doing and take up another task (speak to the person on the other end of the line). This is the same process the PC uses to alert the CPU that a task must be performed. The CPU, upon receiving an interrupt, makes a record of what the processor was doing at the time and stores the information in the “stack”; this allows the processor to resume its predefined duties after the interrupt is handled, exactly where it left off. Every main subsystem in the PC has its own interrupt, frequently called an IRQ (short for Interrupt ReQuest).
2.4.4 WHY USE AN ISP?
An Interrupt Status Port (ISP) is a
The ISP is at Base+7 on each port (Example: Base=280 Hex, Status Port=287, 28F...etc.). The
Example: This indicates that Port 2 has an interrupt pending.
Bit Position: | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
Value Read: | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 |
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