User`s manual

4,291,198
19
character that is also used for a hard key function used
as described in Table II, such a character is handled as
earlier described before returning to the PI level. That
is, the ASCII key actuation is recognized and causes the
process to send to the host computer the escape charac
ter (illustratively backslash " ") followed by the par
ticular ASCII character (Table II, line 8:3); and the
process returns to the PI level. If the ASCII interrupt
character is recognized, the process resets the data
buffer to the all-zero condition and returns to the Pl
level. If any other ASCII character is recognized, it is
transmitted to the host computer via UART 89; and the
process traverses to the PI level to execute the PPI step.
FIG. 15 illustrates the details of the PPI step of the PI
iteration of FIG. 14. The PPI process also services
station set user inputs and comprises a sequence of oper
ations wherein various user related functions are polled.
In a ?rst of these functions, the process determines
whether or not an operation-timing capacity has been
called, generally by the host, by inserting a “t“ in the
string of Table I command "u". If operation timing is in
effect, the process displays on screen 13 the elapsed
time of a user operation, e.g., a user originated tele
phone call; and in so doing it repeatedly checks to deter‘
mine whether or not one second has elapsed since a
prior check on the timing operation. If it has, a seconds
counter in the processor 43 is reset and appropriate
ASCII code is generated to update the elapsed time
display on the bottom line of screen 13. After doing
that, or if less than one second had elapsed, or if the
timing function was not in effect, the process traverses
back to the PPI level to take the next step of the se
quence.
The second step of the PPI sequence is the HARD
KEY process in which the actuation of a hard key on
the keyboard is debounced prior to utilization (soft key
and ASCII key actuations in the illustrative embodi
ment are advantageously debounced by a separate hard
ware chip not shown rather than by using the software
operation here illustrated in FIG. 15). In performing the
debounce operation, the “current" key contact state,
the "last" state prior to the present hard key check, and
a “stable" state immediately prior to the aforemen
tioned last state are checked. If the current state is dif
ferent from the stable state but the same as the last state,
the process recognizes that a new stabilized character
value is present, sets the aforementioned stabilized value
to be equal to the last value, and sends the same charac
ter value (after any translation according to Table II) to
the host computer. Upon completion of that function,
or if the initially received hard key character had been
the same as the stable value, the process returns to the
PPI level. However, if the initially receive key charac
ter were different from both the stable value and the last
value, the process recognizes that the key state is unsta
ble, sets the last value equal to the current value, and
returns to the PPI level.
The next step in the PPI sequence is to examine the
state of the handset, i.e. the switch hook, to see whether
or not to change the set of a timing flag which indicates
whether or not the timing operation is running. If the
handset is on-hook, the process presumes that it had
been off-hook earlier and clears the timing flag. After
this or if the process had found the handset off-hook
earlier, the process assumes that any timing in effect
should remain so and returns to the PPI level to con
sider the next step in the sequence.
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45
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55
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At the duplex step, the last step in the PPI sequence,
the FD/I-ID option switch is compared with its previ
ous state. If it has changed, the set is put in the mode
given by the current switch state. From that point, the
process returns to the PI level of the chart of FIG. 14.
Here a new PI iteration is begun. The previously de
scribed succession of events for the charts of FIGS. 14
and 15 repeats over and over again until the processing
of the data buffer produces a usable exit character that
allows the PI iteration to be terminated and allows the
process to read out a corresponding exit character to
the PEI point in one of the charts from which the PI
function had been called. That exit character is used to
determine the next selection to be executed in the PEI
iteration. That selection execution is followed by either
another repetition of the PEI iteration or traversal to a
higher level as may be appropriate for that selection.
In FIG. 9, the SET PARAMETERS selection is
called by the Table I op-code “s“ and is used to make up
the Table II for further operation of the station set in
conjunction with a host computer. This operation in
cludes a two-component sequence, the ?rst component
is the PEI iteration and the output of that iteration
identifies one of two possible selections. If the PEI exit
character is a control message directing termination of
the SET PARAMETERS operation, it indicates that
the changes in entries in Table II have been completed;
and the process traverses to the PCM level of FIG. 9.
On the other hand, if the PEI output character indicates
some other message, a two element sequence is initiated
to determine which line of Table II is involved and
enter the received character. A subroutine is also in
cluded for spelling (encoding) certain control charac
ters so their function is not actually executed during
writing of the Table.
Further, in FIG. 9, the POSITION CURSOR opera
tion is also illustrated and represents a sequence called
by the Table I op-code “x". This operation is required
during writing of text on the screen 13 and is used to
develop signals to prepare processor 43 to put a charac
ter in a desired screen location. The ?rst step in the
sequence is to remove the cursor from the screen, and
the second is to register in processor memory a two
character message (line number and character position
number) from the host de?ning the new cursor location.
Thereafter VRAM 59 is directed to place the cursor on
screen 13 in its new location, and the next step of the
sequence involves traversing to the SCROLL mode
wherein a character will be written at the new cursor
location.
FIG. 10 illustrates the LABEL KEY sequence in the
FIG. 9 selection. This sequence, called by one of Table
I op-codes a-l, is used to write labels on the screen 13
adjacent to the respective keys 16. The sequence is
repeatedly employed by the host when directing dis
plays such as in FIG. 8. The particular key involved is
identi?ed by the format of the command as indicated in
Table I. The first step is to clear the screen at the indi
cated key label position. Then the PEI iteration is per
formed to obtain a character naming one of three selec
tions. One selection recognizes an ASCII character to
be written and places the character on the screen 13 on
either the left hand or the right hand side and corre
spondingly justified with respect to the screen margin.
After that placement the process returns to PE]. An
other possible selection is a control message indicating
termination of the label operation and causing the pro
cess to traverse to the PCM level in FIG. 9. Ifany other