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XR16C872

Dual UART with 1284 Parallel Port and Plug-and-Play Controller

Exar Corporation 

XR16C872

Preliminary

Manual Configuration Mode Interface

The 872 provides an input pin (MAN#) to bypass the

auto configuration procedure. It changes address lines

A12-A15 to manual configuration inputs S1-S4 and

LPT. These inputs can be designed with external

jumpers to select COM1-COM4 for the serial ports, and

LPT1 or LPT2 for the 1284 printer port.

Manual configuration mode supports the standard PC

COM and LPT port addresses and associated IRQ.

However, the address lines can be mapped to other

memory space areas for embedded applications, more

on this later. The 872 eliminates the external address

decoding logic circuitry that is typically required.

The manual configuration is selected by making the

MAN# pin logic 0 (GND). This changes five address

lines to become configuration inputs. The manual

configuration is accomplished by decoding the PC ISA

bus address bits, A3 through A10 inside the 872 for

chip select. These addresses select the UART for

standard PC COM ports: COM-1, COM-2, COM-3,

COM-4 and LPT-1 and LPT-2. Five inputs (S1-S5) are

generally externally jumper or wired to logic 1 or logic

0 for the operating port. The configuration inputs are

also associated with a given PC interrupt. The mapping

for the COM port 1-4 and their associated interrupt

selections are listed in Table 1. Besides the COM port

addresses, the 872 also decodes two parallel or printer

addresses.

The chip can be mapped into an embedded system

memory space. Figure 4 shows an example of wiring

S1-S5 for default port configuration with IRQA and

IRQB for the two UARTs, and IRQC with DREQ, and

DACK for the parallel port. Address lines A3-A10 are

connected to the embedded system address lines A8-

A15 instead, mapping it to address location 0x7F08-

7F0F, 0x5F00-5F08, and 0x6F00-6F08 respectively.

Application note #xxxx describes how to design with

manual configuration mode in more detail.

MAN# S1 S2 S3 S4 S5

A3-A9 COM Port IRQ Device Selected

0

00xxx

3F8-3FF

COM-1 IRQ4 UART Channel A

0

10xxx

2F8-2FF

COM-2 IRQ3 UART Channel A

0

01xxx

3E8-3EF

COM-3 IRQ4 UART Channel A

0

11xxx

2E8-2EF

COM-4 IRQ3 UART Channel A

0

xx00x

3F8-3FF

COM-1 IRQ4 UART Channel B

0

xx10x

2F8-2FF

COM-2 IRQ3 UART Channel B

0

xx01x

3E8-3EF

COM-3 IRQ4 UART Channel B

0

xx11x

2E8-2EF

COM-4 IRQ3 UART Channel B

0

xxxx1

378-37F

LPT-1

IRQ7 1284 Parallel Port

0

xxxx0

278-27F

LPT-2

IRQ5 1284 Parallel Port

x: don't care

Table 1. Manual Configuration Mode Internal Addess Decode

Rev. P1.00

14

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