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U S E R GUIDE
The IMSAI SIO 3 oard provides 2 independent channels of
serial data input and output.
USART devices, the SIO Board provides 2 channels o f RS232,
TTL, and current loop data lines w ith complete control
signals.
T h e SIO Board also includes all logic necessary to control
the 8251 devices from the IMSAI 8080 Back Plane.
Fo r reference information on the programming and operation
of the 8251 chip, the user should refer to the Intel 8080
Microcomputer Systems User's Manual.
The U s e r 's Guide is intended to cover the information
b eyon d that contained in the Intel Data Book necessary to
m a k e full use o f the SIO b o a r d . ,
Both the memory-mapped and jumper-wired I/O configurations
use the lower 4 bits of the address bytes
to select and control the b o a r d 's functions.
7 o f the b oa r d address
described o n another page.
to run as an input a nd output port type board, then AQ -
form a complete address.
to respond to memory-mapped I/O, then AO - A7 form the
lower byte of. address and the upper by t e o f address is h e x
_FF or octal 376.
Address bits 1 and 2 select serial I/O channel A or channel
B respectively.
serial I/O channel A is enabled.
is on, serial I/O channel B is enabled.
Address b i t 0 determines whether the .1/0 channel selected
will respond to the current byte as a control b yt e or a
data byte.
are selected, and if address bit 0 is a 0, the b yte is
assumed to be data.»
serial I/O channel A, the lower 4 bits of address would
normally contain hex 3 or octal 03, while the normal address
20
9
(A4 - A7) are jumper-selected as
If the b o ar d is jumper-selected
That is, w hen address b i t 1 (Al) is high,
If address bit 0 is a 1, the control functions
Thus, to write a control b yte into
SIO 2 Board Kev. j
User Guide
Edition 2
Utilizing the Intel 8251
(A1 through A3)
If the b o a r d is jumper-selected
W h e n address b i t 2 (A2)
B i t 4 through
A7
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