XR16C872 Datasheet, PDF (10/60 Pages) Exar Corporation – DUAL UART WITH 1284 PARALLEL PORT AND PLUG-AND-PLAY CONTROLLER

XR16C872
DISCONTINUED
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 2 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. 1.00
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