XR16C850_05 Datasheet, PDF (10/56 Pages) Exar Corporation – 2.97V TO 5.5V UART WITH 128-BYTE FIFO

XR16C850
2.97V TO 5.5V UART WITH 128-BYTE FIFO
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REV. 2.3.1
2.2 PC MODE
The PC mode interface includes an on-chip address decoder and interrupt selection function for the standard
PC COM 1-4 ports addresses. The selection is made through three input signals: S1, S2 and S3. The selection
summary is shown in Table 1. Although the on-chip address decoder was designed for PC applications
ranging from 0x278 to 0x3FF, it can fit into an embedded applications by offsetting the address lines to the 850.
An example is shown in Figure 5 where the UART is operating from 0x80F8 to 0x80FF address space.
Operating in the PC mode eliminates external address decode components.
TABLE 1: PC MODE INTERFACE ON-CHIP ADDRESS DECODER AND INTERRUPT SELECTION.
SEL# INPUT
S3, S2, S1
INPUTS
A3-A9 ADDRESS LINES TO
ON-CHIP DECODER
COM/LPT PORT
SELECTION
IRQ OUTPUT SELECTION
0
000
0x3F8 - 0x3FF
COM-1
IRQB (for PC’s IRQ4)
0
001
0x2F8 - 0x2FF
COM-2
IRQC (for PC’s IRQ3)
0
010
0x3E8 - 0x3EF
COM-3
IRQB (for PC’s IRQ4)
0
000
0x3F8 - 0x3FF
COM-4
IRQB (for PC’s IRQ4)
0
100
0x2F8 - 0x2FF
COM-1
IRQA (for PC’s IRQn
0
101
0x3E8 - 0x3EF
COM-2
IRQA (for PC’s IRQn)
0
110
0x2E8 - 0x2EF
COM-3
IRQA (for PC’s IRQn)
0
111
0x3F8 - 0x3FF
COM-4
IRQA (for PC’s IRQn)
0
X XX
0x278 - 0x27F
LPT-2
N/A
0
XXX
0x378 - 0x37F
LPT-1
N/A
FIGURE 5. PC MODE INTERFACE IN AN EMBEDDED APPLICATION.
D0
D1
D2
D3
D4
D5
D6
D7
A0
A1
A2
A3
A4
A5
A6
A7
A14
A15
AEN#
IO R #
IOW #
IN T
RESET
Em bedded Application set to operate
at address 0x80F8 to 0x80FF
VCC
GND
GND
D0
D1
D2
D3
D4
D5
D6
D7
A0
A1
A2
A3
A4
A5
A6
A7
A8
A9
AEN*
IO R#
IO W #
IRQ A
IRQ B
IRQ C
S3
S2
S1
RESET
VCC
TX
RX
DTR#
RTS#
CTS#
DSR#
CD#
R I#
OP1#
SEL
GND
VCC
10