User`s manual

Chapter 5, Interfacing Notes
The Model 9000 is surprisingly easy to interface and there are
several methods of handshaking which can be utilized if it is desired
to operate at the higher baud rates. The following section describes
some of the methods. Of course if you are going to use our interface
program PGMX, you can skip this chapter.
1. Software handshake. This is perhaps the easiest method of all.
When you begin to send data to be programmed, send the first byte
but don’t wait for it to be echoed. That would effectively cut your
communication rate in half. Instead, send the second byte, receive
the first, send the third byte, receive the second, etc. This technique
will allow you to program as fast as the algorithm in use permits.
Some devices program faster, some slower! See an example of this
in Fig. 5.1.
2. CTS/DTR hardware handshaking. The Model 9000 is configured as
data terminal equipment, which means that the CTS (clear to send)
line is an input to the programmmer which when pulled low forces
the programmer to stop sending. On the other hand, the DTR (data
terminal ready) line is an output from the programmer, which will go
low when the buffer is about 50% full and high again when the buffer
is about 38% full. If you are using hardware handshake and the DTR
line goes low, you should stop sending to the 9000 within about 2
character periods (before XOFF is sent). The RTS line is pulled high
whenever the programmer is plugged in. See Specifications for
Cable.
3. Xon/Xoff software handshaking. If you do not monitor the DTR line,
the 9000 will transmit an Xoff character if the buffer gets to be about
63% full. If an Xoff has been sent, an Xon will be sent when the buffer
level drops to about 25% full. Likewise, when the programmer is
sending you data, you may send an Xoff character, which will stop
the programmer from sending until it receives an Xon character.
Xon’s and Xoff’s, are not put into the buffer, but are processed as
soon as they are received. Even if you don’t use Xon/Xoff handshak-
ing, you will find it useful when using the L, list command, to stop
and start the data flow to your screen. Xon and Xoff are the keyboard
equivalents of control–Q and control–S respectively.
Model 9000 Interfacing Notes Chapter 5
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