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Simtel MSDOS 1992 September
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Simtel20_Sept92.cdr
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msdos
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sysutl
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com3_4.arc
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COM3&4.DOC
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1988-12-09
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You can have up to two serial ports on your I/O Card. These
serial ports support asychronous communication functions.
And, these ports can be set to COM1, COM2, COM3 or COM4.
The current release of PC or MS DOS recognizes COM1 and COM2.
Therefore, the current PC DOS (MS- DOS) only performs I/O
functions COM1 and COM2. Unfortunately, DOS can not recoginze
COM3 or COM4;i.e., input and output operations can not be
performed by using COM3 or COM4.
Two new serial port utilities enable COM3 and COM4 to perform
the same functions as COM1 and COM2. One is DEVCOM.SYS, a driver.
The other is CMODE.COM, a utility program.
1. DEVCOM
DEVCOM is a device driver that initializes two devices,
COM3 and COM4, for serial ports on your I/O Card. After
DEVCOM has been executed, you can gain access to these
serial ports by simply entering the names COM3 and COM4.
Before starting DEVCOM, please set your I/O Card's serial
ports to COM3 and COM4. If the system fails to set these
COM ports, the following message will appear on the screen:
Can not find device COM n
To execute DEVCOM, you must copy the DEVCOM utility onto
your current working drive or DOS diskette. The utility is
entitled, DEVCOM.SYS. This device driver sets the COM
parameters into the memory reserved for the operating system's
data and gives you the interface between DOS and BIOS. The
DEVCOM.SYS utility must be set into your CONFIG.SYS device.
If your boot diskette or current working drive has a
CONFIG.SYS device, please add the following command:
DEVICE = DEVCOM.SYS
If your boot diskette or current working drive does not have
a CONFIG.SYS device, create one which includes the previous
command.
With your amended current working DOS diskette in the current
working driver, reset the system. You can reset the system by
pressing the RESET buttom; simultaneously pressing CTRL, ALT
and DEL; or turning the power off and on. If COM3 or COM4 ports
exist, then the following messages will appear on the screen:
Device COM3 is installed.
Parameters set to 2400, n, 8, 1
Device COM4 is installed.
Parameters set to 2400, n, 8, 1
NOTE: A DEVCOM DEFAULT SETS COM3 AND COM4 COMMUNICATION
PARAMETERS TO BAUD RATE 2400, NO PARITY, 8 DATA BITS
AND 1 STOP BIT.
If COM3 and COM4 ports do not exist, then the following
messages will appear on the screen:
Can not find device COM3.
Can not find device COM4.
NOTE: WHEN USING PC/MS DOS VERSION 3.3+, THE DEVICE DRIVER ALONE IS
SUFFICIENT AND THE DOS MODE COMMAND CAN BE USED TO SET ALL THE
SERIAL PORT OPTIONS AS NORMAL, EXCEPT A BAUD RATE OF 19,200.
HOWEVER A 19,200 BAUD RATE CAN BE SET USING THE CMODE.COM.
2. CMODE COMMAND
The utility programm, CMODE.COM, sets options for an
asynchronous communications adapter. The CMODE.COM also
enables printer output to be routed to an asynchronous
communications adapter or to another printer port.
2.1 Setting Parameters
The command format for setting the options of an asynchronous
communications adapter is listed below.
CMODE COMn:baud[,parity[,data bits[,stop bits[,p]]]]
The variable "n" can be 1, 2, 3 or 4 designating the number
of the asynchronous communications adapter.
The protocol parameters used to initialize the asynchronous
communications adapter can be set by replacing the "[" symbols
with specific characters. These parameters and the specific
characters are listed below.
Baud Rate: Enter 50, 75, 110, 134.5, 150, 300, 600, 1200,
1800, 2000, 2400, 3600, 4800, 7200, 9600, or 19200.
The default setting is 2400.
NOTE: ONLY THE FIRST TWO CHARACTERS ARE REQUIRED, SUBSEQUENT
CHARACTERS ARE IGNORED. FOR EXAMPLE, IF THE COMMAND
FORMAT WAS "CMODE COM3: 13,7", THE MODE OF OPERATION
WOULD BE 134.5 BAUD RATE, EVEN PARITY AND STOPBIT
PARAMETERS WOULD DEFAULT SINCE NO CHARACTERS WERE ENTERED.
Parity: Enter N (None), O (Odd), E (Even), M (Mark),
or S (Space).
The default setting is E.
Databits: Enter 5, 6, 7 or 8.
The default setting is 7.
Stopbits: Enter either 1 or 2.
The default setting is 2 if the baud rate
is less than or equal to 110.
The default setting is 1 if the baud rate
is greater than 110.
The "P" option indicates that the asynchronous adapter is
being used for a serial interface printer. If you enter the
"P", time-out errors are continously retried. You can stop
the retry loop by pressing Ctrl-Break. To stop the time-out
errors from being continously retried when you have entered
"P", you must reinitialize the asynchronous adapter without
entering the "P".
2.2 Routing Printer Output
The command formats for directing parllel printer output to
an asynchronous communications adapter or to another printer
are listed below.
CMODE LPT#: = COMn
CMODE LPT#: = LPT$
There are three variables in this command format. The variable
"#" can be 1, 2, or 3 designating the printer port number. The
variable "n" can be 1, 2, 3 or 4 designating the asynchronous
communications adapter. And, the variable "$" can be 1, 2, or
3 designating another printer port.
All output direct to the printer LPT# is redirected to the
asynchronous adapter n, or to another printer $. Another format,
CMODE LPT#: =LPT#, disables any redirection to the printer
designated by the "#".
Before you can use the CMODE to redirect the parallel printer
output to a serial device, you must initialize the asynchronous
communications adapter by using the CMODE COMn format described
in Section 2.1 Setting Parameters. If that serial device is a
printer, your seial initialization command should also include
the "P" parameter.
NOTE: WHEN USED IN THE CMODE COMn FORMAT WITH THE "P" OPTION, OR
IN THE CMODE LPT#: = COMn OR CMODE LPT#: = LPT$, THE CMODE
COMMAND CAUSES THE PRINTER AND ASYNCHRONOUS COMMUNICATIONS
ADAPTER INTERCEPT CODE TO BE MADE RESIDENT IN MEMORY.