Subject: Equipment for a PC/FlexNet-Digi
A typical PC/Flexnet-Digi site consist of a PC with multi
serial ports connected via serial cables to tnc's running
a special KISS EPROM called 6pack. Before you can select the hardware equipment needed to build or convert from a
NetRom site you need to be sure you understand
Site design considerations:
FlexNet is a polling system with a configuration rule
that must be followed to insure proper operation. When designing your configuration you must keep in mind that
the RS-232 baud rate used on any of the PC serial ports
and on it's associated TNC terminal port(s) must equal or
exceed *twice* the sum of baud rate used on all the TNC
Radio port(s).
A FlexNet 6pack software driver which is used within the FlexNet-Digi for each virtual channel which are called
ports, communicates with each TNC running a program
called 6pack.bin contained within the TNC EPROM. The 6pack EPROM is a special KISS
EPROM with additions that allow FlexNet links to operate faster.
A single TNC can be connected to a single PC serial port.
Up to six TNC's can be wired in series and connected to a
single serial PC serial port. As an example a TNC running
9600 on it's radio port would need a TNC terminal port
and PC serial port baud rate of 19200. Six TNC's
connected in series all running 1200 on their radio ports
would need 1200 X 6 = 7200 x 2 = 14400 which is not a
standard value so again 1920 would be needed for the TNC(s)
and PC serial port baud rate. Not all TNC terminal ports
or PC serial ports are capable of 19200 baud. See
paragraphs below for details. Remember 9600 radio links
need 19200 terminal and PC serial port baud rate. If the TNC or PC serial port baud rate limit is 9600 then only
four TNC's with 1200 radio baud rate may be used in
series. If any one of TNC's in series fails they all fail.
Although using the series configuration does save PC
serial port requirements this config may not be a good
idea at a remote site. This is a decision to be made by
the Sysop based on local conditions.
Computer selection:
PC FlexNet software can run on about any PC with the DOS
operating system. That includes an XT. Most of the flex
systems here in the Greater New York region are running
on yesteryear PC's such as 386/486, sx/dx, 20-33 or higher. At some sites FBB PBBS are run as applications on
the same machine. For this a 66 Mhz 486 does well. The
combination Flexnet-Digi/FBB works well and is very
stable. Some of these are running at remote sites with
use of both the FlexNet and FBB remote sysop features. An
example is WT3V on top of the blimp hangar at NAS
Lakehurst NJ.
Memory. FlexNet can operate in the conventional 640k area
of memory. No other memory needed. If FBB operating on
same machine then up to 16 megs can be used but 4 to 8
meg will do the job. FlexNet runs in normal memory with
some modules loaded high. FBB version 7.00 using DPMI
must be used. FBB uses some of normal memory to load then
runs in extended memory.
Drives. The machine should have one 144 floppy and a
Flexnet-Digi can operate with just that. It is better to
run a small hard drive which are common in the older
machines. Flexnet writes current network status data to
disk every few minutes. We have never had a hard drive
problem even at the coldest mountain top sites such at W1TOM
Chester, MA. A larger hard drive for a Flex/FBB system
can't hurt.
For remote site in a small cabinet it is not necessary to
operate with a keyboard and monitor. All commands can be
done over the air by the Sysop using a valid password. A
keyboard /monitor can be brought to the site for a config
change such as adding a port or local RF testing etc. If
the system is to be operated without a keyboard connected
make sure the machine will boot. Some bios can select
bypassing the no keyboard error. If you can't find a
machine that will boot without the keyboard remove the
guts from an old keyboard and install it inside the
computer case.
Serial ports:
Older PC serial cards and serial ports on mother boards
used 8250 uarts. These are not suitable for operation
above 9600 baud. Later model card and mother board serial
ports use 16550 uarts which are OK above 9600. If you
buy new multi port serial cards make sure they use 16550
uarts. Make sure you know what kind of uarts you have and
follow the rule explained above concerning radio vs
terminal/PC serial port baud.
If you are going to operate a Flexnet_Digi needing a lot
of serial ports you can get up to nine by using two multi
port cards plus one of the lower com ports on a regular
card or mother board. See below. That kind of a system
should stay away from newer machines with plug and play
bios unless it can be disabled. A newer machine is great
for a flex/fbb machine requiring only a few serial ports.
The multi port cards we have been using for our NetRom
HUB config and now our FlexNet config are made by SIIG
Inc. Fremont, CA. USA.
HighSpeed/Hi-IRQ I/O, I/O Expander 4S
Current versions can address up to 12 ports Com-1 thru
Com-12. Older versions could address only 8 ports COM-1
thru Com-8. All can select all irq's that could be
available. That is 3, 4, 5, 7, 9, 10, 11, 12 and 15.
The basic card includes support for the 4 ports but comes
with only 2 16550 Uarts installed. Current models have
two DB-9 (male) connectors on the back. Older models have
one DB-9 (male) and one DB-25 (male) on the back. This
card sells retail for $39.95. To add the other two ports
an upgrade kit is required. I/O Expander 4S Upgrade Kit.
That includes the other two 16550 Uarts and the cable
assy for the other two ports. Like the basic card,
current
models have two DB-9 connectors and older models one DB-9
and and one DB-25 Connector. Retail on the upgrade kit is
$28.95.
The older model addressing only 8 ports will do the job
we need done in most of the time. There is one issue to
be taken into consideration. The newer machines may have
COM-1 and COM-2 on the mother board. Also many machines
use multi I/O cards that support the two com ports, the
printer port, game port,
the floppy and IDE drives. We have found that although
the two com ports on the mother board or multi card can
be disabled, they are not. We have run into problems when
trying to use COM-1 and COM-2 addresses on the Hi speed
card with the others disabled.
Please note that we want the 16550 Uart performance and
sometimes the older regular cards do not have them. The
SIGG card that does support the 12addresses does come in
handy when using two cards to get 8 ports and avoiding
the normal COM-1 and COM-2 addresses. This is not
necessary if you can find a only IDE card (no serial or
game port) for the drives.
Serial Cables.
Standard serial cables available from computer stores can
be used for connecting the PC serial port to the TNC
terminal port. They can also be fabricated using only
three wires. RXD, TXD and ground. Other RS-232 functions
not used. The series config can easily be wired from one TNC to another.
TNC selection:
TNC's to be used for a Flexnet-Digi must be what is known
as TAPR, TNC-2 compatible to be able to operate with FlexNet 6pack code contained in an
EPROM. The most common
of these are the AEA PK-80, PacComm TNC-200, Tiny-2,
Spirit and the MFJ 1270 series. All of these have a 1200
baud radio modem and 9600 daughter board modems can be
installed. The Spirit modem is on the main board starting
at 4800 baud. Unfortunately the 6pack code is not
available for Kantroncis TNC's therefore they cannot be
used.
Open squelch DCD boards should be installed on all 1200
baud TNC's.
The original TNC-2 design used in the PacComm TNC-200
and and MFJ TNC's does not support 19200 terminal baud
rate. As such without modification they cannot be used at
the 9600 RF baud as explained above. Fortunately they can
be easily modified to run 19200 terminal baud rate.
For the best performance TNC-200, early model Tiny-2 and
MFJ TNC's should be upgraded to run 9.8 MHz. clock. The
19200 terminal rate also results when this upgrade is
done. Upgrade kits are available from PacComm. 9.8 MHz
clock is standard on later model Tiny-2 and all Spirit.
6pack EPROM.
All 6pack EPROM are the same. The EPROM is a type 27C256.
A speed of -12 or -15 is ok for TNC's with 9.8 clock. I
can burn them for you if required. The image 6pack.bin
comes with the FlexNet software.
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