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B.1
Communication parameters
baud rate
The transmit speed between two serial
ports.
parity
The parity
bit is
used in
error detection. Three different settings are used, which
are ODD, EVEN, and NONE parity.
data bits
The number of bits
in each transmitted or received serial character.
Either 7 or 8 data bits can be specified.
stop bits
The stop bits is used
to detect where
one character ends and another starts. Either 1
or 2 stop bits can be specified. When stop bits is specified then stop bits are generated or checked in the transmit or
receive data respectively. IRQ specifies
which interrupt
is emerged when the
character is received from serial port.
interrupt vector
The interrupt vector is a global interrupt indicator which is designed at several multi-serial adapters (such as four serial card,
eight serial card ... etc.) to
check which serial port emerges interrupt.
Since several serial ports are designed at one adapter and use the common IRQ, so that interrupt vector
is useful to detect
which port emerges interrupt. For example, suppose interrupt vector address of hardware adapter is set to 2C2H, the relationship
between each port corresponds to the
interrupt indicator is shown in the
follows. If you specify this interrupt vector address, when interrupt
is emerged, device driver may check address 2C2H to find
which port emerges interrupt.
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bit 0
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port 1
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bit 1
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port 2
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bit 2
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port 3
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bit 3
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port 4
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bit 4
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port 5
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bit 5
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port 6
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bit 6
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port 7
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bit 7
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port 8
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The standard COM1 and COM2 need not interrupt
vector. We will list several famous multi-serial adapters in
the appendix D.
modem control register
The contents of the modem control register are indicated and described
below.
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bit 0
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DTR
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bit 1
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RTS
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bit 2
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OUT1
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bit 3
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OUT2
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bit 4
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LOOP(0)
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bit 5
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0
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bit 6
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0
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bit 7
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0
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The bit 0 (DTR)
and bit 1 (RTS)
are hardware handshaking. To let PCCOM in the normal mode, you must set the bit 0
and bit 1 to 1. The
bit 4 provides a loopback feature for diagnostic testing of
the serial port. In this case, you must
set bit 4 to be 0. OUT1 and OUT2 are auxiliary user designed output which is used to enable/disable interrupt in most adapters, so
that you must control OUT1 and
OUT2 carefully to let your serial port emerges an interrupt. You may set OUT1=0 and OUT2=1 to enable interrupt of the most
standard COM1 and COM2 adapter, however
some adapters may not work in this case, you can ask
OUT1 and OUT2 control from origin hardware
manufacturer or trial and error to find one of four combination (0,0), (0,1),
(1,0), (1,1).
Appendix D will list OUT1 and OUT2 signal of our multi-serial
family. Some 8250/16450 chip will generate OUT1 = 1 and OUT2 =
1 when internal loop is selected (bit 4
is set to 1), so that they will not emerge
an interrupt when internal loop feature is test.
active status
The active status is
used to specify activation
status of interrupt vector. Either active low or high can be
set. If active low is specified, when the corresponding bit of interrupt vector is 0, means the
corresponding port
emerges an
interrupt, otherwise if the bit is 1, means no interrupt
is active.
XON/XOFF
XON/XOFF
is software handshaking, which is used to prevent the
lost of data while
communication between two serial ports. Suppose we
connect two computer named local
computer and
remote computer,
if local computer is too busy
to receive data
from remote computer, it
send XOFF (S/CTRL whose code is 17) to remote computer to notice he is in busy mode. When remote computer receives XOFF, it will stop transmission
until the local computer sends XON (Q/CTRL
whose code is 19) to continue transmission. The same manner is activated at remote computer.
DTR and DSR
The DTR/DSR is hardware handshaking.
Data Set Ready(DSR) indicates that the modem or data set is ready to establish communications link and transfer data with the serial interface. Data Terminal Ready(DTR) informs the modem or
data set that the serial interface is ready to communication.
RTS and CTS
The RTS/CTS is hardware handshaking.
Clear To Send(CTS) and Request To Send(RTS) can be used to establish communication
protocol. RTS informs
the modem or data set that the serial interface is ready to
transmit data.
B.2
Serial Ports status
The serial ports
status are described in the following.
Carrier Detected
The modem
status which provides
Data Carrier Detected(DCD) to indicate the voltage
level of the associate RS232 line.
Ring Indicator(RI)
Indicates that a telephone
ring signal has been received by the
modem or data set.
Txmtr SR
Transmitter shift
register of 8250/16450 chip.
Txmtr HR
Transmitter holding register
of 8250/16450 chip.
Break Received
Indicates whether the received data input is held in the spacing state
for longer than a full word transmission time, that is, the total time of start bit + data
bits + parity bit + stop
bits.
Framing Error
Indicates that the received character did not have a
valid stop bit.
Parity Error
Indicates that the received data character does not have the correct even or odd parity.
Overrun Error
Indicates that data in the receiver buffer register was not ready by the processor before the next characters was
transferred into
the receiver
buffer register, thereby destroying the previous character.
Receiver DR full
Received Data Register full. If the flag always set, it means the RS232 port hang up
because no interrupt generated when data arrive. Please restart our computer when error occurs.
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