User`s manual

6 Hardware Information

6.1 Port Addressing

The QSP-200/300's four asynchronous serial ports are implemented using 4 standard

16C550 UARTs. Each of these UARTs requires 8 bytes of I/O space and when enabled

which requires the QSP-200/300 to be located on an even 32-byte (20H) boundary (e.g.

300H, 320H, 340H, etc.).

Base Address + 24

Channel D

Base Address + 16 Channel C

Base Address + 8Channel B

Base Address + 0

Channel A

Address assignment

QSP-200/300 channel

6.2 Scratchpad / Interrupt Status Register

Each 16C550 UART contains 8 I/O registers. The last of these registers, located at (Base

address + 7), is referred to as the 'Scratchpad Register' and provides no functionality to

the UART. In place of this Scratchpad Register, the QSP-200/300 implements an

interrupt status register which can be accessed at (Base address + 7) of any UART. The

purpose of the interrupt status register is to give the software programmer an easy way

to inspect the interrupt state of the entire QSP-200/300 with a single input operation.

The format of the interrupt status register is shown below:

Intr

D0D1D2D3D4D5D6D7

When one or more UARTs have interrupts pending, the associated bit(s) in the

interrupt status register are set to logic 1. When all the pending interrupts have been

serviced for a specific UART, its interrupt status bit will be cleared to logic 0

automatically. When all the pending interrupts from all UARTs have been serviced,

the entire interrupt status register will return logic 0. The application program should

not exit its interrupt service routine until all pending interrupts from all channels have

been serviced (interrupt status register = 0) or no additional interrupts will be received.

If an application requires the UARTs' Scratchpad Registers, the interrupt status register

can be disabled. Disabling the interrupt status register is supported by the

QSP-200/300 configuration software, which is operating system dependent. Refer to

the relevant operating system installation section for specific usage of this feature.

QSP-200/300 User's Manual 36