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2006-10-19
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Club 100 Library - 415/939-1246 BBS, 937-5039 NEWSLETTER, 932-8856 VOICE
Documentation for XMODEM, for TRS-80 Model 100
Version of 1/23/85 by Rick Perry
This program performs auto-dial-redial, auto-logon, terminal
emulation, and buffered text file transfers (.DO) using either regular
ASCII Xon/Xoff protocol or the Xmodem Christensen checksum protocol.
Communication parameters are 8N1D during Xmodem file transfers and 7I1E
for terminal emulation and Xon/Xoff transfers. The program will operate
using the 300 baud internal modem or an external modem (Novation
Smart-Cat or equivalent) at 300 or 1200 baud. Files may be Up/Down
loaded directly from/to RAM, disk or cassette.
AUTO-DIAL/LOGON:
The program starts with a "Find:" prompt and will attempt to retrieve
a phone number and auto-logon sequence from the ADRS.DO file and logon
to a host computer.
When using the internal modem, if no carrier is detected within 20
seconds after dialing, or if you press any key, the program will hang up
the phone. After waiting 20 seconds more, it will retry the number
unless you press any key.
If the carrier is detected, it will BEEP and proceed through the
auto-logon sequence as specified in the ADRS line, then jump to the
terminal emulation mode of the program.
At the "Find:" prompt, enter a string to search for in the ADRS file
or press F8 (or enter "Menu") to return to the Menu. When the string is
found press "M" to begin auto-dial using the internal modem, or press
"S" to dial through an external Novation Smart-Cat modem at 1200 baud,
or press "3" to use Novation at 300 baud, or press ESC to return to the
"Find:" prompt, or press any other key (like ENTER) to continue
searching.
If you wish to manually dial a telephone number, enter "Dial" at the
"Find:" prompt. After dialing and hearing the carrier tone, press "M",
"S", or "3" to allow the program to Connect, or press any other key to
return to the "Find:" prompt.
For a Novation Smart-Cat modem, "3" actually sets the modem baud rate
to 300, "S" sets it to 1200, and the modem command character is set to
CTRL/V in both cases. The modem is also set for 8-bit data format and
"unlisten" mode to allow Xmodem transfers. Note: modem baud rates, cmd
char, etc. are not affected when using "DIAL" option at Find: prompt.
The control sequences used with the Novation modem appear around the
last twelve lines of the program. This code may be modified to work
properly with other smart modems. When dialing through an external
modem, code around the last eight lines of the program allow you to
directly enter commands to the modem and optionally press CTRL/R to
restart the program or CTRL/E to exit to the Menu.
TERMINAL EMULATION:
Once in terminal emulation mode, the program is transparent to all
control characters entered from the keyboard (except CTRL/G as noted
below) and these characters (like CTRL/C/S/Q) will be sent to the host.
But Function key F5 (Brk) may be used to STOP the program if needed.
F4 (Term) is used to jump directly to TELCOM's Term mode while
remaining connected to the host. Once in TELCOM you cannot return to the
program without logging off and disconnecting from the host unless you
are connected through an external modem.
F6 (Free) provides a display of how many bytes of RAM are currently
available.
F7 (Dir) lists the RAM file directory in the same way as the BASIC
FILES command.
F8 (Bye) is used to exit the program and return to the Model 100's
Main Menu.
F2 (Down) will initiate a file download transfer and F3 (Up) will
initiate uploading.
F1 (Prev) will display the previous screen, same as in TELCOM.
FILE TRANSFERS:
After pressing F2 or F3 and entering file name, program prompts
"Append?" if downloading. Then it prompts "Use XMODEM protocol?" --
press "Y" or "N". Responding with "N" means that buffered Xon/Xoff
protocol will be used.
For uploading using Xon/Xoff protocol answer "Width?" prompt by
pressing ENTER if no wrapping is desired, otherwise enter desired width
for word wrapping.
During Xon/Xoff download, F3 is blanked and F2=@@@@. Press F2 to end
download. During upload, use F8 to abort.
DOWNLOADING WITH XMODEM PROTOCOL:
The host should be ready to send the file before entering this mode.
While downloading, the received file is not displayed on the screen.
When a NAK (negative acknowledge) is sent, the program prints an "X".
When ACK (acknowledge) is sent, the program prints ".".
You can abort the download at any time by pressing F8 (Abrt). The
program itself will automatically abort the download only if one of the
following circumstances occur:
- The host sends a CANcel.
- The received block number is neither the current block number nor the
previous block number.
- An error trap occurs in the program (this could be caused by an "Out
of Memory" condition on the Model 100).
UPLOADING WITH XMODEM PROTOCOL:
The host should be ready to receive the file before entering this
mode. While uploading, the transmitted file is not displayed on the
screen. When a NAK is received, the program prints an "X". When ACK is
received, the program prints ".". If nothing is received after waiting
10 seconds, or if anything other than NAK, ACK or CAN is received, the
program prints a "?".
You can abort the upload at any time by pressing F8 (Abrt). The
program itself will automatically abort the upload only if the host
sends a CANcel or if an error trap occurs (e.g. due to an IO Error when
uploading from cassette).
ALTERNATE CHARACTER SET:
When in terminal mode, press CTRL/G to switch between the regular
character set and an alternate set (pseudo APL). This character
translation is defined in an array, T(*), which is loaded from the last
data statement. This only affects characters printing on the screen,
not file transfers.
PROGRAM NOTES:
The program itself does not count the number of NAK's sent or
received per block and will not automatically abort if an excessive
number of NAK's occur. It is up to you to use F8 (Abrt) to cancel the
file transfer if you feel that too many NAK's are occuring.
When aborting a file transfer the program sends a single CANcel
character (CTRL/X) to the host and returns to its terminal emulation
mode. If you then notice that the host has not responded to the CANcel,
you may send additional CAN's by pressing CTRL/X. Some hosts expect to
receive three CTRL/C chars in a row to signal an abort; that's dumb, but
anyway, if CTRL/X doesn't work, try that. Most hosts will automatically
abort an Xmodem transfer if no chars are received for 1 or 2 minutes.
MAXFILES is set to 3 at the beginning and reset to 2 upon normal exit
to the Menu.
Function key definitions are restored to their previous user-defined
values upon exit from the program to the Menu.
The following ROM calls and POKEs are used:
6118 - set serial interface parameters and activate modem.
16969 - turn cursor on.
17061 - set and display temporary function key strings.
17875 - fill previous screen with blanks.
21172 - keep phone off hook.
21179 - hang up phone.
21264 - 2 second delay.
21274 - 1/2 second delay.
21293 - dial a phone number.
21392 - execute auto-logon sequence.
21608 - jump to TELCOM's Term mode.
21795 - display previous screen.
27804 - restore function key definitions.
POKE 63056,64 - enable scrolling into previous screen area and also
disables Break and ON KEY and makes F1...F8 return chars 248...255.
POKE -86,0 - purge keyboard buffer.
PERSONAL NOTE:
This program is customized for my own use, so some of its features
may not be useful to you. In particular, note that it performs CLEAR
500, MAXRAM and leaves MAXFILES=2. Feel free to revise the program to
your own liking and share it here and/or elsewhere.
MACHINE LANGUAGE SUBROUTINES:
The integer array M(0)..M(60) is used to hold six position
independent machine language subroutines. Entry points are at M(0),
M(3), M(16), M(21), M(24) & M(59). The assembly source listing follows:
; ENTRY M(0) - check MDM: for carrier detect.
; calling sequence: CALL VARPTR(M(0)),0,VARPTR(X)
; where X is an integer variable.
M(0) call 6EEF ; check for carrier detect
mov m,a ; X=0 if carrier detected,
ret ; FF if no carrier
nop
; ENTRY M(3) - convert string to uppercase.
; calling sequence: CALL VARPTR(M(3)),0,VARPTR(A$)
; where A$ is a string variable.
M(3) mov a,m ; check length of string
ora a ; if zero
rz ; then return
mov c,a ; save length in counter C
inx h ; get string address
mov a,m ; that's the low byte
inx h
mov h,m ; that's the high byte
mov l,a ; HL --> string
lxi d,2 ; here comes the tricky part
call 31E9 ; in ROM there is XTHL, PCHL
$PC1 dad d ; now HL = loop
pop d ; and DE --> string
loop ldax d ; A = char from string
call 0FE9 ; let ROM convert to uppercase
stax d ; restore converted char
inx d ; point to next char
dcr c ; decrement counter
rz ; done when counter = 0
pchl ; otherwise jump to loop
; ENTRY M(16) - check MDM: or COM: queue for received chars.
; calling sequence: CALL VARPTR(M(16)),0,VARPTR(X(0))
; where X(0)..X(1) is an integer array.
M(16) mvi m,0 ; set flag, X(0)=0, for no char
call 6D6D ; check queue for chars
rz ; return if no chars available
inr m ; set flag, X(0)=1, for char received
inx h
inx h ; HL --> received char buffer, X(1)
nop
; ENTRY M(21) - retrieve char from MDM: or COM: queue.
; if entry was made at M(16) and the queue contained a char
; then the code will fall through to this point and the
; received char will be placed in X(1).
; M(21) may also be called independently of M(16) to receive
; a char if it's already known that one is there (due to an
; ON MDM GOSUB.. interrupt for example).
; calling sequence: CALL VARPTR(M(21)),0,VARPTR(X)
; where X is an integer variable.
M(21) call 6D7E ; get char from queue
mov m,a ; store it
ret
nop
; ENTRY M(24) - timed read of 131 chars from MDM: or COM: queue.
; calling sequence: CALL VARPTR(M(24)),0,VARPTR(Z(0))
; where Z(0)..Z(131) is an integer array.
; Z(0) is used as a flag.
; Upon return, if Z(0)=0 then a timeout occurred.
; Z(0)=1 implies successful return and in this case
; Z(1)..Z(131) will contain the 131 received characters.
x1 equ 39. ; get_ch - $PC2
x2 equ 7. ; ck_que - $PC2
x3 equ 4. ; init - $PC2
M(24) mvi m,0 ; set flag for failure
mov d,h
mov e,l ; DE = HL --> flag
call 31E9 ; xthl, pchl
$PC2 mvi b,131. ; char counter
push b
push h
; stack now contains:
;
; address of flag
; char counter
; sp --> $PC2
init lxi h,7282. ; HL = 1 second timeout counter
ck_que call 6D6D ; check queue
pop b
push b
push b ; extra $PC2 on stack
xthl ; counter on stack, HL = $PC2
lxi b,x1 ; offset to get_ch
dad b
xthl
rnz ; jnz get_ch
pop b ; clear stack
dcx h ; decrement timeout counter
mov a,h
ora l
pop b
push b
push b ; extra $PC2 on stack
xthl ; counter on stack, HL = $PC2
lxi b,x2 ; offset to ck_que
dad b
xthl
rnz ; jnz ck_que
pop b
pop b
pop b
pop b
ret ; timeout exit
get_ch call 6D7E ; get char from queue
inx d
inx d
stax d ; store it in buffer
pop h
pop b
dcr b ; decrement char counter
push b
push h ; HL = $PC2
lxi b,x3 ; offset to init
dad b
push h
rnz ; jnz init
pop h
pop h
pop h
pop h
inr m ; set flag for success !
ret
; ENTRY M(59) - delay A*2 milliseconds
; calling sequence: CALL VARPTR(M(59),A
; where A is an integer from 0 to 127.
M(59) mov c,a
jmp 531C
TIMING COMPARISONS:
Up/down-loading tests were performed using a 3422 byte text file and
a VAX-11/780 host. The following table shows the relative time required
for the file transfers normalized to the TELCOM download time at 300
baud (which was 114 secs.). Alternate character set was not used, nor
was word wrapping, and CAS: times include overhead of opening the file:
-------XMODEM PROGRAM-------
Xon/Xoff Xmodem
baud direction TELCOM RAM CAS: RAM CAS:
300 down 1.00 1.25 1.89 1.02 2.16
300 up 1.25 2.28 2.98 1.52 2.14
1200 down 0.46 1.27 1.89 0.76 1.38
1200 up 0.58 2.25 2.93 0.75 1.41
CONCLUSIONS:
- In TELCOM, uploads take about 25% longer than downloads.
- 1200 baud transfers take at best only half as long as 300 baud,
partly due to the slow speed of LCD scrolling. Using Xmodem program
Xon/Xoff protocol, transfer times are independent of baud rate.
- Transfer times for Xmodem protocol using RAM file are slightly longer
than TELCOM times. Using CAS: file doubles the time in some cases.