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CO2JA > BPQ 06.01.97 13:16l 160 Lines 6538 Bytes #-10893 (0) @ WW
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Read: DG2VY DJ5QY DD6ZJ DG0LGF DG0OAW OE6KAF VK3EUB SP6ASD DL8HK GUEST
Subj: AX25.COM Docs Part 1/2
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Sent: 970103/0404Z @:CO2JA.#HAV.CUB.NA #:28920 [La Habana] FBB5.15c $:28920_CO2
From: CO2JA@CO2JA.#HAV.CUB.NA
To : BPQ@WW
AX25 driver for BAYCOM-like modem.
Version of 4th of January 1992, Pawel Jalocha, SP9VRC
Free license for this software is granted for _amateur_ use only.
Commercial usage is prohibited.
AX25.COM is a packet driver comforming (to some extend) to well known
"FTP packet driver specification". It's purpose is to serve as interface
between application software (e.g. KA9Q NOS) and a modem connected
to RS232 port (e.g. BAYCOM modem).
The driver relies on the following RS232 pins:
RTS - controls PTT: high level activates the transmitter
DTR - transmitted data. On this pin the driver sends data
to be transmitted by the modem.
When in receive state this pin is held high.
CTS - received data. The modem should supply here the data it receives.
DCD - the modem may supply here "carrier detect" signal.
This pin is _optional_ - it is not a must because the driver
is able to deliver carrier signal from received data.
GND - a common ground for the above signals.
TxD outputs a signal which is in high (positive voltage)
most of the time. A low power modem (TCM3105) can be supplied
from RTS+DTR+TxD (adding realized with diodes).
My primary intention while writting this driver was to provide
opportunity to run KA9Q NOS with simple modems based on TCM3105
or AM7910 chip. I tested the driver _only_ with NOS - no other software
was available at the time. Thus I can not guarantee full compatibility
with "FTP packet driver" definition.
The driver status can be examined with PKSTAT.COM and the driver can be
terminated (removed from memory) by TERMIN.COM. These two utilities
are part of packet drivers package from Clarkson and they should work
with any "FTP packet driver".
AX25 driver heavily relies on quick interrupt response.
Thus the application software should avoid disabling
CPU interrupts for long periods. Or say it in another words:
enable interrupts whenever possible.
AX25.COM has several start-time options. To see them start it
with "-?". If you start the driver without any command line
switch it will use default values: COM1, 1200 baud, etc.
These are the options - default values are in []:
-b<bit rate> [1200] - decimal number
defines the bit rate. Rates below 300 are not accepted
because of PC's timer specific features.
Maximum usable rate is probably 2400 but it really depends
on your CPU... The upper limit for this parameter is 14400.
"Valid" rates are only numbers which can be expressed as 14400/n.
If you give an "invalid" value it will be adjusted to the
closest "valid" one.
-i<software interrupt> [60] - hexadecimal number
Tells the driver which software interrupt to use
for control functions. Usually you would use numbers
from 60..63 here because these are intended for user
applications.
-B<COM port I/O base> [3f8] - hexadecimal number
I/O address of RS232 port: 3f8 for COM1, 2f8 for COM2
-I<COM port IRQ> [4] - hexadecimal number
Interrupt request line of RS232 port: 4 for COM1, 3 for COM2
Only the range 2..7 is supported so far. I'm not sure the irq 2
would work on a PC/AT.
After IRQ number you may add letter "p" (like: -I4p).
This will make the selected IRQ priority highest in the system.
This may help XT users to get the driver working
- the future will verify this.
Normally IRQ0 (system timer) has highest priority.
-s<slot time> [120] - decimal number 16..255
Slot time for p-persistance scheme. The value is in data bits.
For 1200 baud, slot time 120 bits means 100 ms.
-p<persistance> [64] - decimal number 0..255
p-persistance - the higher the value the higher the probability
of activating PTT at a time slot.
Your station becomes more "agressive" on the air
with increasing persistance and decreasing slot time.
-h<tx header length> [240] - decimal number 8..65535
Number of extra bits the transmitter sends before actuall data
is transmitted. This is same as TxDelay on most TNCs.
240 bits means 200 ms at 1200 bps.
You should always make this number as small as possible
for best bandwidth use. 240 tells you that many "useless"
bits (30 bytes) are being transmitted before real packet data
goes out.
Unlike most TNCs this driver sends a square wave not a series
of HDLC flags in front of a packet. This was easier to program
in software and it makes DPLL lock faster at receiving end.
Thus less header bits should be needed...
-t<tx tail length> [24] - decimal number 8..65535
Number of extra bits the transmitter sends _after_ the actual data.
24 bits makes 20 ms tx tail.
-c<carrier sense mode> [t] - one of the following letters: f,c,t,d
mode meaning
f full duplex - transmit whenever data is pending.
This option disables carrier sensing.
c sense modem DCD line to find out whether channel is busy or not.
Your modem has to supply this signal. Note that TCM3105
does not do it very well... it sets DCD to high on any noise
on audio input. Am7910 is said to deliver much more reliable CD
signal.
t sense data transition - if incoming data signal moves
the driver assumes that the channel is busy - BAYCOM 1.5 uses
the same (or very similar) way with "CARRIER 1" switch.
Use this mode if you intend to use squelch in your radio.
d deliver "channel busy" status by analysing incoming data.
BAYCOM's v1.5 "CARRIER 0" does effectively similar thing although
it uses different algorithm. The driver examines the incoming
signals "regularity" - if data transitions comes at regular
intervals the channel is assumed busy.
With this mode you may run your radio with squelch open
all the time.
How this option works may depend on modem type. Some modems
have still very regular digital output signal even with white
noise applied to the analog input.
-T<DCD threshold> [50] decimal number 0..100
Threshold for software DCD (acts only when -cd option is selected)
The higher the number the "clearer" the signal must be to trigger
"channel busy" status. You should lower this number if your station
tends to transmit over others.
-S enable sound effects - when a valid frame is received you will
hear a short (1/18 sec) beep from PC's speaker.
Please note that argument line is case sensitive and so are hexadecimal
values... "2F8" will not do - you must specify "2f8".
--- continued on part 2/2
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