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Calculators: Desktop: Rockwell 320

(c) Emil Dudek 2011

Size (approx):

224mm x 244mm x 75(max)mm (w,h,d)
Weight 1225g excluding cable and plug


Mains (230V 50/60Hz, 2.6W) power only through an IEC320/IEC60320-C13 three-way mains cable (computer/kettle type).
Display: 12+symbol digit green VFD: the symbols (to the far left) are used for memory, error and negative indication. 
Features: Standard four functions with selectable floating/fixed decimal modes and switched rounding modes, six function memory, register exchange, percentages and item count. Semi-RPN logic.
Age: 1976
Manufacturer: Rockwell International, Microelectronic Product Division, Anaheim, CA 92803, USA, made in Japan. Serial number 528187N.


A sturdy, large desktop from the early 70s which has a few extra useful functions.  The logic is quite good with good recovery and no obvious bugs.

Case and Design: Of three-piece construction made from matt light and dark grey plastic, which is quite wide.  The top of the case has a sophisticated cooling grid to keep the dust out.  A heavily inset and (almost vertical tilted) green plastic display filter gives a bright and high contrast display, and has a silver Rockwell logo. There is a deeply inscribed model number in the keyboard area.

Keys and Switches: The keys in olive, grey, dark grey, cream and red are grouped by function. They are  long travel with a chunky hollow-sounding clunk on pressing and return.  The oversized zero and decimal key rather spoil the symmetry though.  The rounding switch has white raised lettering.  The on/off switch is situated on the right hand side, nearly at the top.
Construction: Remove the four screws from the rear, flip the calculator over and lift off the front, hinging around the bottom edge.

Boards: The main board is fixed to the rear of the case by four screws.  It holds a small display board (RK320-340403A PIX-10) which is mounted on metal brackets. This is connected to the keyboard assembly via 16 yellow wires and an earth wire. The latter is fixed to the front section with numerous screws and sturdy metal braces.  There is a small mains transformer and fuse holder mounted separately.
Components: 1 x cpu: Rockwell A4540CB 7620 (week 20 of 1976), 42 pin staggered DIL, 0.6" width grey ceramic with metal cap
3 x display drivers(?): Toshiba TM4358P 6-F (June 1976), 16 pin DIL, 0.3" width black plastic
1 x IC: Toshiba TM4352P 6-E (May 1976), 16 pin DIL, 0.3" width black plastic
1 x 12 digit + symbol green VFD display, single tube flat glass face
3 x transistors
23 x diodes
3 x capacitors
18 x resistors
7 x resistor arrays
1 x fuse
1 x mains transformer (H0-70 28T6Z T)

Logic comments: (C/CE) is used to clear the calculator and or as a Clear Entry function for multiply and divide
Input overflow is suppressed: keying a thirteenth digit is ignored
The display shows commas for thousands indication
Negative numbers are shown with a minus in the far left (symbol cluster) digit thereby allowing full twelve digit negative numbers
There is automatic constant on divide and multiply only
Fixed decimal modes are selected by (DEC SET)(n) where n is one to eight, nine selects fully floating
There is a rounding switch for round down (v), round up (^) and round (5/4)
The logic is semi-RPN (Reverse Polish Notation) to do 2-3 key in (2)(+)(3)(-)
The key (N COUNT) will return the number of items added or subtracted in a chain
Divide by zero shows "0."  and (<-) in the far left symbol cluster and is recoverable using (C/CE)
Overflow shows the result shifted and (<-) in the far left symbol cluster and is recoverable using (C/CE)
The (EX CHANGE) keys allows to to swap primary and secondary registers
Memory storage is indicated by an "M" in the far left symbol cluster
(M*) is memory recall and clear, whilst (M) will recall only.  The (=+) and (=-) key will force the result of a calculation and add/subtract to memory
Overflow in memory is flagged, is recoverable using (C/CE) and maintains the original number
No bugs found