Bit Counter - Raytheon DIDS-400 Series Technical Manual

DIDS-402-2AMI3
4 - 18. 4 Bit C oun te r
The bit counter consists of three flip-flops connected in a divide- by-eight
countdown circuit. Three outputs are produced by the bit counter;
a. CTS - The cursor time slot timing pulse is the timing equivalent to
the cursor bit. From previous discus sions, the cursor is a moveable
bit in memory which is attached to the LSB of a data character. The
CTS output is primarily used to either locate the cursor or cause
an operation to be performed in coincidence with the cursor.
b. CTS +1 - The cursor time slot plus one timing signal occurs in
coincidence with the least significant data bit of a character and is
used primarily to enable data transfers through the buffer registers.
c. CTS +4 and 5 - This timing pulse is decoded for use in conjunction
with the monoscope Ishift-off-screen' circuitry. ,,·When
a
NULL
character is detected in the character readout register (indicating
that a standard letter, numeral or symbol will not be displayed),
the monos cope beam is positioned to a small box ( . ) symbol at the
edge of the target. The purpose of this decoded output is to limit
the monoscope active scan interval to four bit times. This prevents
'burning' the frequently used symbol and thereby lengthens the usable
life of the monos cope tube.
The decoded CTS pulse is one bit time in width and occurs once every 13 f.ls.
CTS is used within the timing circuitry to clock the eight-character and binary
counters. For a timing relationship between the bit counter outputs and memory
data, refer to figure 4-20.
CHARACTER '4'
C
U
1M
1 L
~
S 1 I I
l i s 10 1
I B 1 I I 1 1 I BI R 1
I I I
I I
1°111110110 OIRI
I
I I I
I
II
I I
l.JLIl.UL
I
I I : :
I I I
n
CTS I
!
~
- _ _ _ --,r-t...,1 I
I
CTS+l
~
ICTS+ 2)
___ . . . . . n . . . . __
'CTS+ 3)
__
~n
. . . . . __
C""T=-=S--+--4-, ' : :' : CT=-=S--+-=-5 ~
010\ 68-519
NOTE: PARENTHESES DESIGNATE
OUTPUTS NOT DECODED
BY TIMING CIRCUIT
Figure 4-20. Bit Counter Outputs and Memory Data Relationship
4-45