User`s manual

4,291,198
17
At line 8:0 in Table II, a value of NULL (0), e.g.,
in a table provided by a new host, indicates that the host
does not support this feature, and the set processor will
then suppress transmission of the key activation to the
host if the user calls for it.
The “pad character” mentioned in Table II at the line
B=5 is a nondisplay ?ller sent by host when it needs a
delay without disturbing its peripheral units. The sta
tion set learns during initializing handshake with host
what the character is. When the pad character is re
ceived by the set processor, it is ignored. This allows
the host to implement timing delays by emitting a num
ber of pad characters.
FIGS. 9 through 15 represent the operation of pro
cessor 43 depicted in the form of program structure
charts. These charts show what the processor does in
recurrent cycles of operation, and they are readily un
derstandable to programmers skilled in the art. Such
charts are prepared in accordance with a technique
called "hierarchical structure." This technique is ex
plained in detail, for example, in Chapter 2 of Principles
of Program Design by M. A. Jackson, Academic Press,
New York, 1975. Each process charted ?ows from top
to bottom as illustrated in the sense that for a block at
any given level in a chart, the details of the operation
performed by that block are depicted in one or more
blocks in one or more lower levels of the chart con
nected thereto by lines in the chart.
Components of a chart include elementary compo
nent blocks which have no parts; and, after each execu
tion of the portion of the process represented thereby,
the process returns to the next point requiring further
execution in a higher level from which the process
under consideration was called. In addition, the pro
if)
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gram structure charts include three composite types of 35
components. One of the composite types is indicated by
a small zero in the upper right hand comer of each
block of this type and it indicates a selection is to be
made among blocks of the same type at the same level
in the diagram. On completion of the selected block
execution, the process returns to the next higher level
requiring further processing. A second composite type
is indicated by an asterisk in the upper right hand corner
of the block and is an iteration. A function represented
by such a block occurs zero or more times; and if the
blocks of the next lower level are of an unmarked type,
the functions of those lower level blocks are executed in
recurring sequence from left to right as illustrated until
a termination function is attained in some lower level
block. Then the process returns with the termination
exit information to the higher level at which the itera
tion was called and proceeds in accordance with the
exit information. The third composite type of compo
nent is indicated by a block having only the name of the
function to be performed and no special marking in the
upper right hand corner thereof. This third type is
called a sequence and indicates that blocks of the same
level and appended to the same higher level block are to
be executed in a sequence extending from left to right as
illustrated one time, and then the process returns to the
next higher level requiring further execution.
Several additional schematic conventions are to be
noted. The term “PUT" in a block label means to put a
character under consideration on the display screen 13.
The term “SEND" means to send the character under
consideration to the host computer through the UART
89. Any character string beginning with STX (meaning
start of text) and ending with CR (meaning carriage
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55
60
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return) is a status message and indicates that the process
must collect certain information, determined by the
location in the process at which the message is used, and
transmit it in the character string to the host computer.
SCROLL moves all lines of text on the screen 13 up one
line and clears the bottom line. SCROLL can occur
only when in the SCROLL mode and with the cursor
on the last line of the display. Figure references con
tained within a block indicate the ?gure where process
details are shown. The term RESET indicates an opera
tion which clears the text displayed on screen 13 and
causes the process to go to the SCROLL mode.
Processor 43 recurrently operates in accordance with
the chart of FIG. 9. Thus, in PROCESS CONTROL
MESSAGE (PCM) the processor obtains a control
message from its internal data buffer (not separately
shown) and executes one of the seven selection type
functions illustrated in the second level from the top in
FIG. 9. These selection functions correspond to the
Table I processes. The process then returns to the data
buffer to obtain a new control message. Each of the
selection processes in the second level of FIG. 9 is indi
cated in more detail either in FIG. 9 or in one of the
FIGS. 10 through 13. In the latter ?gures, the same
selection block of FIG. 9 is repeated at the top of the
chart in the further ?gure to provide convenient cross
reference.
FIG. 9 and each of the charts in the FIGS. 10 through
12 include an iteration block PROCESS EXTERNAL
INPUTS (PEI) which is depicted in greater detail in
FIG. 14 and in still further detail in FIG. 15. These
latter two ?gures will be discussed before proceeding
further with FIGS. 10 through 12. The PEI process
includes within itself a further iterative process desig
nated PROCESS INPUTS (PI) as shown in FIG. 14.
The latter process services external inputs by the station
set user via the keypad or by the host via UART 89.
The ?rst function of the PI iteration processes the data
buffer of processor 43 to look for inputs received by
way of UART 89 from the host computer in accor
dance with an interrupt operation. Thus, any time that
data from the host appears in the UART, processor 43
interrupts its other operations to load the data into its
data buffer. If the buffer is empty when checked per
FIG. 14, the process returns to P1 to pick up the next
step of the iteration. If the buffer is not empty, the data
buffer character which is ready for processing is taken
from the buffer; and the entire PI iteration is terminated
by exiting to the calling function to perform the opera
tion named by the exit character, i.e., the selection of
one of the functions in the level below the PEI block of
the chart from which the PI function was called.
The second step of the FIG. 14 PI iteration is a PRO
CESS KEYPAD operation in which processor 43
checks the keypad to determine whether a hard key or
a soft key or an ASCII key had been actuated. If a soft
key is involved, a control character operation is indi
cated, and the processor 43 translates the key output
character into a corresponding three-character string
and sends it to the host computer. The string includes
the STX character followed by a character, such as a
TABLE I label op-code, and further followed by the ‘
CR character. This identi?cation of a soft key to the
host effects host program mode selection as outlined in
regard to FIG. 8. The process then returns to the PI
level in FIG. 14 and commences execution of the PRO
CESS POLLED INPUTS (PPI) step of the iteration.
On the other hand, if the keypad output were an ASCII