ST16C650A
2.90V TO 5.5V UART WITH 32-BYTE FIFO
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REV. 5.0.0
2.1.1
PC MODE
The PC mode interface includes an on-chip address decoder and interrupt selection function for the standard
PC COM 1-4 port 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 650A. An
example is shown in Figure 6 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.
S3, S2, S1
INPUTS
A9-A3 ADDRESS LINES TO
ON-CHIP DECODER
COM/LPT PORT
SELECTION
SEL INPUT
IRQ OUTPUT SELECTION
0
0
0
0
0
0
0
0
0
0
0 0 0
0 0 1
0 1 0
0 0 0
1 0 0
1 0 1
1 1 0
1 1 1
- - -
0x3F8 - 0x3FF
0x2F8 - 0x2FF
0x3E8 - 0x3EF
0x3F8 - 0x3FF
0x2F8 - 0x2FF
0x3E8 - 0x3EF
0x2E8 - 0x2EF
0x3F8 - 0x3FF
0x278 - 0x27F
0x378 - 0x37F
COM-1
COM-2
COM-3
COM-4
COM-1
COM-2
COM-3
COM-4
LPT-2
IRQB (for PC’s IRQ4)
IRQC (for PC’s IRQ3)
IRQB (for PC’s IRQ4)
IRQB (for PC’s IRQ4)
IRQA (for PC’s IRQn
IRQA (for PC’s IRQn)
IRQA (for PC’s IRQn)
IRQA (for PC’s IRQn)
N/A
- - -
LPT-1
N/A
FIGURE 6. PC MODE INTERFACE IN AN EMBEDDED APPLICATION.
VCC
D0
D1
D2
D3
D4
D5
D6
D7
D0
D1
D2
D3
D4
D5
D6
D7
VCC
A0
A1
A2
A3
A4
A5
A6
A7
A0
A1
A2
A3
A4
A5
A6
A7
TX
RX
DTR#
RTS#
CTS#
DSR#
CD#
RI#
A8
A9
AEN*
A14
A15
AEN#
IOR#
IOR#
OP1#
IOW #
IOW #
INT
IRQA
IRQB
IRQC
Em bedded Application set to operate
VCC
at address 0x80F8 to 0x80FF
GND
S3
S2
SEL
GND
S1
GND
RESET
RESET
10
EXAR [ EXAR CORPORATION ]
