User`s manual

4,291,198
7
arranged so that when actuated its armature strikes a
solid member, e.g., the station set chassis, to provide an
appropriate clicking sound audible to the station set user
upon actuation of any key on the keyboard 20, or associ
ated with display 13, for informing the user that the
processor has responded to the key actuation. Clicker
74 is selectively disabled by software instruction from a
user or a host computer as will subsequently be dis
cussed.
Keyboard 15 includes the various types of set 10 keys
as hereinbefore outlined. Actuations of these keys are
communicated to processor 43 in two different ways.
The soft keys 16 and 23 and the hard keys 30—32 are
connected to processor 43 by respective logic level
signal leads in a twenty-two lead bus 54. Processor 43
recurrently samples the signal states ofthe leads in parts
of the process utilizing the hard and soft keys. The
sampling rate is sufl'icently high to assure detection of
any changes. States of the keys of keyboard 20 are re
currently scanned at all times by a scanner encoder 48,
such as the KR 2376 keyboard encoder chip of the
Standard Microsystems Corp. That circuit provides
clock signals to the keyboard for sequentially sampling
the respective key states, and the samples are returned
to the scanner encoder where an actuated-key sample
causes a 7-bit snapshot of a clock pulse counter to be
applied to a latch 24 to identify the actuated key. The
snapshot is accompanied by an eighth but which gates
all eight bits into the latch. Output of latch 24 is coupled
to processor 43 by way of an eight-bit bus 49. The
eighth bit is used as a flag in latch 24 to signal, when
interrogated by processor 43, that there is information
to be processed. A lead 51 from processor 43 carries
signals which reset latch 24 after its contents have been
read so that a new snapshot can be received. The total
sequence of sampling, snapshotting, reading, and reset
ting occurs more than 50 times per second to be sure
that no keyboard key actuations by even a fast human
user are missed.
Another input to processor 43 provides an FD/HD
(full duplex, half duplex) option signal from a set of
option switches 57 also included in the station set and
available to the station set user for selection during any
particular call connection or other station set use. Still
another lead to processor 43 is a handset hood status
signal OFFHK as provided via contacts H55 in FIG. 4
and which are part of the aforementioned switchhood
associated with the handset 17.
A random access memory display controller VRAM
59, such as the Matrox Electronic Systems Limited of
Canada video random access memory MTX1632A, is
utilized with the microprocessor for exercising control
of the driver circuits for the display screen 13 on cath
ode ray tube 14, FIG. 6. Such driver circuits are not
separately shown but are advantageously those manu
factured by the Electronic Display Division of Ball,
Incorporated. Nine-bit addresses are provided to
VRAM 59 from a data input/output port of processor
43 on a multibit bus 60. Data is provided to the VRAM
59 by way of a multibit data bus 61 extending from a
processor input/output port. Read-out signals are also
provided from VRAM 59 to the processor by way of
the same bus 61 as needed, for example, in a display
scrolling operation. An analog signal output port from
VRAM 59 provides signals on a three-circuit bus 62 for
coupling to the cathode ray tube separate signals for
controlling horizontal de?ection, vertical de?ection,
and beam intensity. The VRAM 59 thus receives from
0
5
25
40
45
55
8
processor 43 signals defining the nature of a particular
character to be displayed and the position on the display
for that character, and it converts that information into
the necessary de?ection and beam control signals to
write that particular information in the particulr region
indicated on the screen 13.
During the course of a communication with the sta
tion set circuits as illustrated in FIG. 4, incoming ring
ing signals are received by way of the circuit 21 to alert
the subscriber. The ringing signals are coupled from the
circuit 21 through a limiting resistor 63 and a direct
current blocking capacitor 66 to be full wave recti?ed
in a bridge rectifier 67. Some of the high frequency
ripple is bypassed by a shunt connected capacitor 68,
and the remaining signal energy is limited in amplitude
by a breakdown diode 69 prior to coupling to a tone
ringing circuit 70 such as one using the S2561 ringer
chip of American Microsystems, Inc. That chip, and
associated resistors and capacitors connected to the
chip in a manner well known in the art, accomplish the
conversion of the ringing signals into the desired ring
ing tone, the latter tone is then utilized to actuate the
loudspeaker 42 for alerting the subscriber.
Assuming an incoming voice signal call, the sub
scriber answers by lifting the handset 17 and thereby
releasing a switchhook actuator (not shown) for allow
ing the various pairs of swtichhook contacts to close.
Two sets of these contacts HS] and H82 close the line
circuit 21 for direct current through to a hybrid net
work 71 which is, in turn, coupled to the handset 17.
The hybrid network 71 is of a type currently in use in
commercial telephone service for coupling the separate
circuits of a receiver 72 and a transmitter 73 to the
two-wire line circuit 21. The hybrid network includes a
hybrid transformer 76 as well as varistor limiting de
vices 77 and 78 and a hybrid balancing impedance 79 in
a common branch of the otherwise separate receiver
and transmitter circuits.
In order to initiate an outgoing call, the station set
user enters calling information using the keyboard 20 as
previously noted. Processor 43 collects the sampled key
information by way of the bus 49 and supplies that
information to the host computer, in a manner to be
described, to be associated with display-position-con
trol address information and returned to processor 43.
Thereafter the sample and position information are
supplied to the VRAM 59 which develops the neces
sary outputs to control the cathode ray tube for writing
corresponding characters in appropriate parts of the
screen 13.
In addition, when the dialing information has been
collected, and if the calling station set subscriber is
off-hook as indicated to processor 43 by closure of
contacts HSS, processor 43 supplies the dialing informa
tion to a tone generator 47 by way of a circuit 50. That
generator is advantageously a Motorola MC14410 2
out-of-8 tone encoder. Generator 47 produces charac
ter-distinctive multifrequency tones corresponding to
the respective dialing characters. Each tone is produced
during a ?xed interval and coupled through a trans
former 80 and the switchhook contacts H81 and HS2 to
the line circuit 21.
When this dialing signal outputting function begins,
the processor 43 also provides a DRELY signal which
actuates a dial relay 81 to close contacts DR1 in series
with a direct current blocking capacitor 82 at the tip
conductor end ofthe secondary winding oftransformer
80 to complete the tone output circuit. Additional dial