ZBasic System Library
194
ZBasic Microcontrollers
Type
Subroutine
Invocation
OpenCom(channel, baud, inQueue, outQueue)
Parameter
Method
Type
Description
channel
ByVal
Byte
The serial channel to open.
baud
ByVal
Long
The desired baud rate.
inQueue
ByRef
array of Byte
The queue for incoming characters.
outQueue
ByRef
array of Byte
The queue for outgoing characters.
Discussion
This subroutine prepares a serial channel for use. If the specified channel number is invalid, the call has
no effect. Serial channels are either implemented in hardware (using an onboard UART) or in software.
Depending on the device one, two or four hardware-based serial channels are supported, denoted by the
channel numbers 1, 2, 7, 8, etc. (Com1, Com2, Com7, Com8, etc., respectively). All ZBasic devices can
support as many as four software-based serial channels, denoted by the channel numbers 3-6 (Com3,
Com4, Com5 and Com6). Note, however, that you must have previously called ComChannels() in
order to use channels 4-6.
The supported baud rates for the hardware-based channels are the standard rates from 300 to 460,800.
Tthe supported baud rates for software-based channels are listed in the table below. However, if
ComChannels() has been invoked, the maximum rate for channels 3-6 will be limited to that specified in
the description of ComChannels(). Moreover, for channels 3-6 the baud rate for any given channel
must be an integral divisor of the maximum rate. Also, for ZX devices running at 7.37MHz, the maximum
software-based channel baud rate is 9600. For generic target devices, the set of desired software-based
channel baud rates must be explicitly specified as part of the device configuration and will be a subset of
the rates in the table below; the baud rates that are attainable with a specified accuracy are dependent on
the operating frequency.
Supported Baud Rates for Channels 3-6
300
600
1200
2400
4800
9600
19200
The transmit and receive queues specified for the channel each must have been previously initialized by
calling OpenQueue(). If you set up a transmit-only or receive-only serial channel you may use the value
0 for the unused queue. If you provide the value 0 for both queues, the channel will not be opened.
After opening the channel, flow control may be configured for either the transmit side, the receive side or
both. See the description of the ControlCom() subroutine for more information.
Example
Dim outQueue(1 to 40) as Byte
Call OpenQueue(outQueue, SizeOf(outQueue))
Call ComChannels(2, 9600)
Call DefineCom(4, 0, 12, &H08)
Call OpenCom(4, 9600, 0, outQueue)
The code above prepares Com4 as a transmit-only serial channel. If you wanted reception as well, you
would have to declare and initialize a second queue and define the receive pin.
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