Vector Graphic Bitstreamer II, User Manual, Page: 13 / 54

The Vector Graphic Bi tstreamer II Board is an all-purpose input/output
board for S-l~~ systems. It offers three serial I/O channels and 2 8-bit
parallel input/output channels for interfacing with multiple peripheral
devices such as printers, modems, and terminals. It also offers a 55 Hz
real-time clock which can interrupt the CPU for functions such as sharing of
the CPU by several users or peripherals.
We will use the term "channel" rather than "port" to avoid confusion
caused by the fact that each serial channel makes use of two I/O addresses,
which are often called I/O "ports."
The CPU sends data to the serial and parallel charmels via I/O addresses.
The I/O addresses used by the board can be changed as a group. The board
uses the eight I/O address x2 to x9 (in hexadecimal notation), where x is
any dig it from 0 to 7. You specify the value of x by jumper, as listed in
Table 1 in Section 2.1. Table 2 in Section 2.1" lists the function of each
of the eight I/O addresses, which are fixed relative to one another.
'!he Bitstreamer II Board does not come wi th any software for specific
applications, though Vector Graphic supplies certain items of software that
make use of its featues.
The three serial channels center around three industry standard 8251
USART (Universal Synchronous/Asynchronous Receiver!Transmitter) chips. Much
of the flexibility of the Bitstreamer II board derives from the flexibility
of these chips, which can be modified via software. You, through software,
can control the rate of transmission, and the format of the transmitted
data. Data is transmitted as ASCII code having bet'II'Ieen 5 and 8 bits per
character, wi th an optional added-on pari ty bi t (choice of even or odd), and
with one start bit and a choice of one, one and a half, or two stop bits per
character. Further, using the 825l's, the board can handle either
asynchronous or synchronous comm.mication. Each serial channel is entirely
independent of the others. Baud rates, format, handshaking, and whether
comnunication is asynchronous or synChronous, is specified independently for
each serial channel through software and in some cases hardware
modifications.
It is not within the scope of this manual to detail the functioning of
the 8251 USART chip, nor to teach the theory of serial communication. In
order to write your own communications software or to modify the Bitstreamer
II serial channels, you will need to be thoroughly familiar 'IIi th this ch ip.
You can refer to Intel's App1 ication Note #16, entitled "Using The 8251
Universal SynchronOUS/Asynchronous Receiver/Transmitter," which Intel will
provide. This Note is also an excellent reference on basic communications.