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ZBasic Language Reference
129
ZX Microcontroller Family
7.5 Setting Device Options
By default, the compiler generates code for the ZX-24 device. The target device may be changed either
by adding a command line option to your project file or by adding a compiler directive to the first module
to be compiled (usually the one containing the Main() routine). Alternatively, you may specify the target
device by using the “Device Options…” entry on the Options menu. The resulting dialog contains a
combobox with entries for the supported devices. This dialog can also be used to update the firmware in
your device or, for some ZX models, to set configuration parameters like the Program Memory EEPROM
characteristics or external RAM configuration.
7.6 Downloading Without Using DTR Signaling
Normally, the process of downloading a compiled program to a ZX device begins with the downloader
toggling the serial port’s DTR line in a designated fashion, causing the ZX device to enter a special
command mode. When the ZX enters command mode in this fashion, it sets the baud rate of the Com1
serial channel to 115.2K baud and waits for commands from the host. Meanwhile, the downloader
changes the baud rate of the PC serial port to match the 115.2K baud rate and then begins sending the
ZX a series of commands to effect the downloading of the compiled program. Finally, when the download
has completed the downloader toggles DTR again causing the ZX to reset and begin running the
downloaded program.
The downloading procedure described above works in most situations but there are some cases where it
won’t work. In particular, if a PC serial channel doesn’t support DTR or doesn’t support toggling DTR
quickly enough to be recognized as the “go to command mode” signal, then the procedure above cannot
be used. Additionally, if the baud rate of the serial channel cannot be changed dynamically (for example
when using a radio link like BlueTooth or XBee), the procedure above cannot be used because of the
required baud rate changes.
In cases where the normal DTR-triggered downloading procedure cannot be used, an alternate procedure
can be used to effect a download. The alternate procedure requires a special configuration of the
downloader and a matching special configuration of the ZX device. Instead of toggling DTR, the alternate
procedure initiates the download procedure by sending a pre-determined character (known as the ATN
character) to the device. The ZX responds to the receipt of the ATN character by entering command
mode (either automatically, or by way of the ZX System Library subroutine ZXCmdMode). Once in
command mode, the downloader can optionally send a command to instruct the device to switch to
115.2K baud for the download; otherwise the downloading is done at the prevailing baud rate. Finally,
once the download has completed, the downloader sends a command telling the device to reset thus
commencing execution of the downloaded program.
The ATN character is set in the ZBasic IDE using the dialog invoked by choosing the Serial Port Options
entry on the Options menu. In the “Download Options” groupbox, you’ll find a checkbox captioned “Use
ATN character”. When that checkbox is checked, two more controls become enabled. The first is an edit
box with an accompanying spin control that allows you to specify the desired ATN character (the range
for which is 1 to 31 decimal). Below the enabling checkbox, another checkbox captioned “Change speed
for download” allows you to control whether the download is done at the prevailing speed (unchecked) or
at 115.2K baud (checked). If you are using a serial channel that does not support dynamically changing
the baud rate, you should uncheck the latter checkbox.
On the ZX side, enabling downloading by way of the ATN character can be accomplished in one of two
ways. The simplest way is to use the directive Option AtnChar in the first module of your program.
Once your program is compiled and downloaded (which, by the way, must be initially accomplished using
the traditional DTR-based method), when the device receives the designated ATN character it will
automatically invoke the command mode. The second method, which should rarely be needed, is to add
code to your application to detect the specified ATN character. When the ATN character is received, your
code should invoke the ZX System Library subroutine ZXCmdMode() either with with no parameter or
with a parameter value of False.
It is important to note that the “Port Speed” setting in the “Execution Options” group box must be set to
match the baud rate of the Com1 serial channel of the ZX device. The default Com1 speed is 19.2K baud
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