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Sharp Compet 363P Programmable Desktop Calculator
Updated 4/22/2004
The Sharp Compet 363P is virtually identical to another machine in the museum, the Burroughs C3660. The two machines are very similar, having only subtle differences in packaging and nomenclature. It is clear that Sharp was behind the design of the Burroughs machine, making a few minor changes for brand differentiation between its own 363P and the Burroughs C3660. This 363P, as well as the Burroughs C3660 in the museum were both built during the mid-1971 timeframe.
Compet 363P (Left) and Burroughs C3660 (Right) Internal Views
Removing the top half of the case (which includes the keyboard assembly), makes it clear that the Sharp 363P and Burroughs C3660 are virtually identical internally. The same group of six Rockwell-made MOS LSI (Large-Scale Integration) integrated circuits make up the calculating brains of the machine. The board layouts are very similar, and the mechanical construction of the machines is identical. The main logic of the machine is spread across four plug-in circuit boards. The circuit boards plug into a hand-wired backplane that provides interconnection between the boards. The four boards seem to be fairly logically divided in their function. One board seems to be related to input processing, such as scanning and encoding of the keyboard, timing generation, and overall housekeeping logic. Another board seems to provide all of the circuitry needed to operate the magnetic card reader/writer. The main logic of the machine is housed on the next circuit board, which also includes the Nixie tube displays, as well as decoder/driver devices that run the Nixies. Lastly, a fourth board seems to provide the programming functions of the machine, including the memory for program steps and memory registers. Aside from the LSI devices, the boards are heavily populated with NEC uPD1xx and uPD3xx-series small- and medium-scale MOS integrated circuits.
Display/Calculating Board(Top), and Programmer/Sequencing Card of the Sharp Compet 363P
The Sharp 363P uses a similar display subsystem to that of the Burroughs
C3660, using sixteen NEC CA-80 Nixie tubes for the numeric portion of
the display. Each of the CA-80 tubes contains the digits zero through nine,
a right-hand decimal point, and a 'tick' located to the left of each digit
for grouping displayed numbers into three-digit groups for easier reading
of large numbers. The machine performs leading-zero suppression, which
helps make reading numbers in the display easier on the operator.
The 363P Nixie Tube Display (Note "ticks" grouping digits into threes) Along with the sixteen Nixies, three
special gas-discharge tubes complete the display panel. The right-most tube
in the display panel is a nine-segment tube, arranged in a narrow 7-segment
rendition with two additional vertical segments bisecting the 7-segment
pattern. This tube is used to display memory register numbers, branch
destination codes, and certain program operation codes. The next tube to the
left is a multi-segment display, in the form of the classic "starburst",
allowing the tube to display stylized alphabetic characters. This tube displays
symbols indicating the operation being performed in programs. Together,
these two tubes are used only when the calculator is in any of the
programming modes. The Burroughs version of the machine dispenses with the
'starburst' tube, opting for individual indicators on the keyboard panel
of the machine for showing the program operation codes. The Burroughs
machine has a slight modification to the 'main board' (the one with the
Nixie tubes and calculator LSI's on it) that adds an edge connector
that brings out the signals to drive the discrete indicators for program
opcode display on the keyboard panel.
Program Function Display Tubes in Operation The left-most tube of the group of
three special tubes is used for sign and error indication. The tube displays
a '-' sign when the number in the display is negative. Below the '-' sign, a
symbol, which lights up in conjunction with the '-' sign to form an 'E',
lights when the calculator detects an error condition. Along with the
'E' indication, the machine lights up all of the ticks in each of the
Nixie tubes to further reinforce the indication of an error condition.
Error indications are triggered by overflow of the machine, illegal
operations (division by zero), or overflowing of the program memory.
Taking the square root of a negative number does not cause an error
condition, returning a negative square root, which is technically
inaccurate.
Sharp 363P Error Indication The Compet 363P, programming functions
aside, provides the basic four math functions and square root. Square roots are
calculated by entering the number to calculate the square root of, pressing
the [÷] key, then pressing the [+=] key to generate
the result. The [X] and [÷] keys contain indicators that light the
function symbol when an operation is pending. For example, when performing
3 X 4, when the user hits the [X] key, the "X" nomenclature in the key will
light up with a red glow to indicate that a multiplication operation is pending.
Once the second number is entered, and the [+=] key is pressed to calculate
and display the product, the "X" indicator is extinguished.
The calculator provides ten
accumulator-style memory registers. There are four keys to the right of the
math function keys that control the memory registers. A given memory register
is cleared (with the [CM] key), recalled (with the [MR] key), subtracted
from (with the [M-] key), or added to (with the [M+] key) with these
keys. When performing a memory function, the memory function key is
pressed, immediately followed by a single digit from zero through
nine to indicate which memory register the operation is to be performed upon.
A special keystroke sequence, [CM] followed by [.], clears all of the memory
registers to zero. Four incandescent indicators on the keyboard panel provide
visual indication of the state of memory registers 1 through 4 (no
status indication is provided for memory registers 0, 5, 6, 7, 8 and 9)
by lighting up when the corresponding memory register has non-zero content.
Detail View of Compet 363P Keyboard (Note Illuminated [X] Key) The other functions of the machine
operate as they do on other Sharp calculators of the time. Addition and
subtraction work adding machine-style, with the [+=] key used for addition,
and the [-=] key for subtraction. Multiplication and division operate as
expected, with the [+=] key generating the answer. A slide switch on the
keyboard panel enables the constant function for multiplication and division.
The [CE] key clears the display register, and the [RC] key
recalls the last operand to the display. The [+/-] key toggles the sign
of the number in the display.
The calculator can operate in fixed
or floating decimal point modes, which is set by two nine-position
slide switches at the left of the keyboard panel.
The 363P provides separate decimal point settings for the display (R) and
for the memory registers (M). Selections are provided for fixed
decimal settings at zero through seven digits behind the decimal point,
or for full floating (F) decimal point placement. The display and memory
registers also have separate settings for roundoff. Two three-position
slide switches select force up, 5/4 (5-up, 4-down), or truncate modes
for rounding of numbers in the display or memory registers.
The operating mode of the machine
is set with a slide switch on the keyboard panel that has five different
settings. "N" (Normal) mode is selected to use the machine
as a normal calculator, with program execution disabled. The "A" (Auto)
position of the mode switch puts the calculator in program execution mode.
In program execution mode, the [+=] key serves as a start key, which, when
depressed, causes program execution to begin (or continue from
a programmed HALT instruction). The "PRO" (Program) position of the mode
switch is used for entering programs into memory. As keypresses are entered,
they are stored in the program memory one step at a time. In program
mode, the Nixie tubes display the current step number, and the
special tubes display the operation code for each key as it is
entered. The "DEB" (Debug) position of the mode switch is used to step
through programs step at a time (with a step executed with each
press of the [+=] key). When in Debug mode, the Nixies display math results
as usual, and the special purpose tubes show the operation code for each
instruction as it is executed. Lastly, there is "CHE" (Check) mode, which
is used for program entry verification. In check mode, the Nixie display
shows the step number, and the special function tubes show each program opcode
as the user moves through the program with each press of the [+=] key, but
unlike Debug mode, when the calculator is in Check mode, the program is
not executed.
The program memory on the 363P has
a capacity of 144 program steps, the same as the Burroughs C3660.
The machine has the capability of eight different conditional branches, and
six unconditional branches within any given program. The calculator uses
tags to mark locations in programs for branching operations to transfer
to. Branching functions are designated by the [J→] (Jump To) and
[→J] (End Jump) keys. The tags consist of the Jump To or End Jump
instruction, followed by a single keypress that indicates the 'tag'.
The keys [0] through [7] and [H] are tags for conditional jumps,
and the [8], [9], [0], [.], [+/-], and [C] keys are the tags for
unconditional jumps. When a branch is needed in a program, the [J→]
key is pressed, followed by the tag key identifying the type and destination
of the branch. When executing a jump instruction, the calculator searches
through memory for an End Jump instruction followed by the same tag key,
and begins execution at the step following the End Jump. In the case of a conditional branch,
the number currently in the display is checked to see if it is zero, and if it
is, the branch is taken to the specified tag, else the tag key is skipped,
and execution continues with the next step in sequence. While searching
for the matching End Jump for
a given Jump To, if the end of memory is reached, searching rolls over to the
beginning of memory, making backwards jumps possible.
Program Operation Code Displays The [H] (HALT) key stops program
execution at the end of a program, or when data input by the operator is
required. Pressing the [+=] key when the machine is halted restarts program
execution at the next step. The machine has the capability for two programs
to be resident in memory at once, with the [PII] key selecting a secondary
program. When the calculator is in Auto mode, program execution
begins when the [+=] key is pressed. If the [PII] key is pressed before
starting a program with [+=], the machine searches through memory looking
for two consecutive "END" instructions, and sets up for program execution to
begin after the last of the two "END" instructions. This capability is useful
for programs that have inverse functions. For example, a program that
calculates the common logarithm of a given number could have the PII program
set up to calculate the anti-log when invoked.
The content of program memory can be
stored on magnetic cards for future use via the 363P's magnetic
card reader/writer. The program memory on the 363P is volatile, meaning
that when the power is removed the content of the memory is lost. When
the 363P is first powered up, program memory is automatically filled with
[H] (Halt) instructions.
The Sharp 363P "Brag Tag" The magnetic card reader/writer,
located at the top left of the cabinet, has a slot that accepts a four-inch
long by two-inch wide magnetic card that has two edges, A and B, for recording
program steps. Each edge holds 72 program steps, for a total
of 144 program steps per card. Notches which can be cut out of each end
of the card cause that edge of the card to be write-protected. Each
mag card comes with a protective paper envelope that holds the card and has
areas on the outside to write information and instructions for use of the
program contained on the card. The card has a surface on
the front (non-oxide) side for writing information about the
information stored on the card. The back side is coated with a magnetic
iron oxide that stores the information in the form of areas of the material
that are magnetized in a North-South or South-North orientation to represent
binary bits. The card reader/writer assembly is made by Sankyo Seiki Co.,
Ltd. of Toyko, Japan. This card reader was a popular choice for calculator
manufacturers, with variants used by Rockwell and Computer Design Corporation
(Compucorp) in their programmable calculators.
Mag Card & Storage Sleeve for Sharp Calculators The card reader is controlled
by three keyboard keys. The [ENTER] key is used for loading
a program into memory, the [RECORD] key for writing program memory
out to a card, and the [VERIFY] key for comparing the content of a card
with memory for verification purposes. The card is placed in the slot
on the top of the machine, and when one of the card reader
control keys is pressed, the card is drawn into the reader by a
rubber wheel driven by a small motor, being read/written on the way in, and
then pushed back out once the read/write operation is completed.
The 363P is a reasonably fast calculator,
with most operations completing almost instantly. The longest operation,
calculating the square root of all-nines, takes less than 1/2 second
to perform. All-nines divided by 1 takes perhaps 1/3 second to complete.
However, as programmable machines go, the 363P isn't terribly fast. A simple
program consisting of a jump tag, followed by [1] and [+=], followed by an
unconditional jump back to the tag (making a tight loop that simply
counts up by one on each loop) executes about 22 counts per second.
Add to Memory Register 1 [M+]
Subtract from Memory Register 1 [M-]
Recall Memory Register 1 [RM]
Clear Memory Register 1 [CM]
End of Program Marker [END]
Branch Tag Marker 1 [→J]
Branch to Tag 1 [J→]
Halt [H]
Multiply [X]
[÷]
Add [+=]
Subtract [-=]
Recall [RC]
Clear [C]
Clear Entry [CE]
Change Sign [+/-]
Decimal Point [.]
Digit 9
Digit 8
Digit 7
Digit 6
Digit 5
Digit 4
Digit 3
Digit 2
Digit 1
Digit 0