3.4
Serial Interfaces
The VP7 serial ports are fully compatible with the NS16450 and NS16550. This means that each serial
interface provides a 16 byte FIFO and therefore offers a higher performance than earlier used standard
serial interfaces. The UARTs have programmable baud rate generators capable of 50 to 115200 baud.
There are four address locations defined for serial interfaces on standard PCs. The serial interfaces are
I/O mapped and can occupy the following address ranges:
Name
Address
COM1
$03F8 - $03FF
COM2
$02F8 - $02FF
COM3
$03E8 - $03FF
COM4
$02E8 - $02FF
Each serial channel provides an identical register set as shown in the table below:
Address Offset
Divisor Latch Bit 1 Name
$00
0
Receiver Buffer (Read)
Transmitter Holding (Write)
$01
0
Interrupt Enable
$02
0
Interrupt Identification (Read)
FIFO Control (Write)
$03
x
Line Control
$04
x
Modem Control
$05
x
Line Status
$06
x
Modem Status
$07
x
Scratch register
$00
1
Divisor Latch (LSB)
$01
1
Divisor Latch (MSB)
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