Dec 222017
 
Fix DTR drop problem w/QBasic 4.5. Debug script.
File FDTR45.ZIP from The Programmer’s Corner in
Category BASIC Language
Fix DTR drop problem w/QBasic 4.5. Debug script.
File Name File Size Zip Size Zip Type
FDTR45.TXT 3840 1331 deflated
TPCREAD.ME 199 165 deflated

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Contents of the FDTR45.TXT file



January 14, 1989


Microsoft's solution to 'fixing' the DTR drop problem with QB 4.5
when closing the communications port by outputing a 3 to the
modem status register, is not a sound or reliable solution.

Many modems simply respond too quickly to the loss of DTR.

The correct solution is to of course not turn DTR off in the
first place. However, after many years and many versions of
Quick Basic, it is apparent that Microsoft either does not listen
to its customers or they simply do not care.

Sound programming practices dictate that when you directly manipulate
a hardware port, you restore that port to the exact same conditions
it had prior to your touching it. In the case of DTR, this means
that if DTR were ON when the QB program loaded, then DTR should
remain ON when the QB program ends. If DTR was OFF when the program
loaded, then fine, turn it OFF when the program ends.

To the end that it is an ongoing struggle to get Microsoft to listen
to the needs of the programmer, the following patches are provided
to enable you to patch your copies of BRUN45.EXE and BCOM45.LIB.


Before beginning, make sure you have backup copies of BRUN45.EXE
and BCOM45.LIB.

BCOM45.LIB DTR Patch
--------------------

With Debug in a DOS path, type :

debug bcom45.lib

Type :

s cs:0 ffff b0 00 e3 01

Debug should show :

xxxx:1529

where xxxx can be any number depending upon where Debug loaded the
program into memory. In any case, the number is not important.

Type :

u 1529

Debug should show :

MOV AL,00
JCXZ 152E
INC AX
ADD DX,+04
OUT DX,AL

This is where QB graciously resets the comm port to parameters it thinks
the comm port should have.

To fix the problem, Type :

a 1529

mov al,01
[Enter]

a 152d

nop
[Enter]

where [Enter] is the Enter key (do not type the characters)!


To verify that you typed everything correctly, Type

u 1529

Debug should show :

MOV AL,01
JCXZ 152E
NOP
ADD DX,+04
OUT DX,AL


To save the corrections Type :

w

Debug should show :

Writing 35EF7 bytes


Now type Q and you are finished patching BCOM45.LIB



BRUN45.EXE DTR Patch
--------------------

First, rename BRUN45.EXE to BRUN45.X

With Debug in a DOS path, type :

debug BRUN45.X

Type :

s cs:0 ffff b0 00 e3 01

Debug should show :

xxxx:9E78

where xxxx can be any number depending upon where Debug loaded the
program into memory. In any case, the number is not important.

Type :

u 9e78

Debug should show :

MOV AL,00
JCXZ 9E7D
INC AX
ADD DX,+04
OUT DX,AL

This is where QB graciously resets the comm port to parameters it thinks
the comm port should have.

To fix the problem, Type :

a 9e78

mov al,01
[Enter]

a 9e7c

nop
[Enter]

where [Enter] is the Enter key (do not type the characters)!


To verify that you typed everything correctly, Type

u 9e78

Debug should show :

MOV AL,01
JCXZ 9E7D
NOP
ADD DX,+04
OUT DX,AL


To save the corrections Type :

w

Debug should show :

Writing 12E80 bytes


Now type Q and you are finished patching BRUN45.X

Rename BRUN45.X back to BRUN45.EXE



The ever powerful Code View debugger was used to to find these
addresses by tracing a QB program which had but two statments :

OPEN com port
CLOSE com port


Any questions may be addressed to :

Kenny Gardner
The Crow's Nest BBS
(714)493-3819

CIS : 76054,210
Genie : K.L.Gardner




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