.he DK-10 Programming             Page 
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.comment harware memo 12
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DK-10 Programming
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1. Introduction
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	The Systems Concepts DK-10 terminal controller provides
direct from memory output and buffered input of characters
at program set speeds from a DEC PDP-10 system.  The following
memo describes the programming of the DK-10 and some
aspects of its operation.
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2.1 Input
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	The DK-10 has provisions for setting the speed of each input line
and for enabling and disabling each input line (see section 3.4).  When
a character is received on an enabled input line it is placed in a
16 slot first-in-first-out stack along with the line number on
which it was received.  A character received when this stack is full
will be lost.
	As long as there is at least one character in the input
stack, the input done flag will be on in the DK-10`s control
register and it will request an interrupt if its PIA is non-zero.
Character and line number pairs may be read in from the stack
by doing a DATAI.  The entire input stack can be cleared by doing a
CONO to clear the input done flag.
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2.2 Output
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	The DK-10 performs character output directly from memory and
handles enough bookkeeping that, for may applications, no output
interrupts need be taken.  The DK-10 has a base address register (see
section 3.2) that is used to access a list of word pairs
for the output lines.  The first word of each pair, at the
base address plus twice the line number, has a count of
characters remaining to be output on that line.  The second word,
at the base address plus one plus twice the line number, is a pointer
to the buffer of characters to be output.  This pointer
is similar to a regular byte pointer with its halves swapped and is
effectively ILDBed by the DK-10 to get characters.  The size field is
always treated and stored back as if it were 7.  The postion
field should be of the form 36-7k.
.figure 5
	When the count word is counted down to -1 for an output line,
the output done flag is set for this line.  If output interrupts
have been enabled, the DK-10 will then request an interrupt and
it will be possible to read in the number of the line that stopped.  The
DK-10 has provisions for starting and stopping each output line and for
setting the speed of each output line be doing CONOs.
	To make it easy to ring buffer output, the DK-10 actually examines
each word that it fetches from memory for the purpose of extracting a character
from it.  If the bottom bit is one (this bit is not used in packed 7 bit fields)
then the word is treated as a new "swapped byte pointer" which is
effectively ILDBed to get the character to output and then stored
back on top of the second word of the word pair associated with this
output line.  Thus one can store a byte pointer back to the start
of a buffer at the end of the buffer.
	If the DK-10 gets a non-existant memory indication on a read or
write or a parity error on a read it sets an error
flag in its control register and stops all output processing until
reset.
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3.1 DATAI
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.figure 2
	14-17 input line on which character was received
	28-35 charcter code
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3.2 DATAO
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.figure 2
	15    if a one, enables output interrupts
	16-35 base address for output control words
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3.3 CONI
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.figure 2
	14-17 number of an output line with done flag set
	27    in on, indicates some output line done
	28    state of selected input line
	29    selected output line busy
	30    parity error
	31    non-existant memory error
	32    input done flag
	33-35 priority interrupt channel assignment
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3.4 CONO
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.figure 2
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	18    master clear
	19    makes function apply to selected line through highest
	20-23 line number
	24-26 speed if used by function
	27-29 function as follows:
	         0 set output done
	         1 start output
	         2 disable input
	         3 enable input
	         4 stop output & clear output done
	         5 set output speed & start output
	         6 set input speed & disable input
	         7 set input speed & enable input
	30    clear parity error
	31    clear non-existant memory error
	32    clear input done flag
	33-35 priority interrupt channel assignment