texas instruments sr-60a - pahhc

Texas Instruments SR-60A Programmable Calculator

Introduction

9/24/11 HHC 2011 Conference 1


Introduction

My name is David Ramsey.


(And this is my first PowerPoint presentation. Be gentle.)


Introduction


I’ve been collecting HP calculators since the late 1970s.



Introduction


I’ve been collecting HP calculators since the late 1970s.

My collection of the scientific handhelds is complete.



Really complete.



My wife is very understanding.



So I started in on the desktops…




No 9100s (yet), but I’m picking up a 9820A here at the conference! <Gloat>



Of course, there’s the whole “running out of room for desktop calcu-lators” thing, but I try to improvise. For example, nothing beats the feng shui of a gracefully-placed 9815A…


But this presentation isn’t about HP calculators. Let’s get to the SR-60A!

(Gene assures me you’re all interested…)

I recently found this calculator on TAS. It was advertised as “Working”, and it was, kind of. The card reader had the gummy wheel we’re all familiar with, and as it turned out there was one bad memory chip.




Warning: I am not an SR-60 expert!


SR-60A Information Introduced: 1976 (SR-60) and 1977 (SR-60A)

Original price: $1695 (SR-60) $995 (SR-60A). The SR-60A was about $3,537.76 in 2010 dollars.

Discontinued: 1979

Memory: 1,200 bytes (SR-60) 3,120 bytes (SR-60A)

CPU: TMC0501 4-bit (also used in many T.I. handhelds)

Keys: 95

Display: 20 character alphanumeric display

Printer: 20 character alphanumeric thermal printer

An SR-60A is just an SR-60 with the optional memory expansion kit.

The first, and only, desktop programmable calculator ever made by Texas Instruments.



Here’s a timeline for the early calculators:



SR-60A Left Keyboard

• Memory Access

• Scientific Functions

• Mode and Printer Control

Note the LEDs above the DEG MODE, TRACE, and LIMITED PRECISION keys.

The X<->K key makes the displayed number a constant; used after the 2nd key, it sets the memory partitioning between registers and program steps.



SR-60A Middle Keyboard

• Numeric Entry

• Parenthesis

• Prompt Response Keys

The SR-60 can handle up to 10 levels of parenthesis.



SR-60A Right Keyboard

• Program Control/Alpha Keys

• Card Reader Control

• Program Step/Editing Keys

Pressing the e1 through e5 keys will jump immediately to that label in memory and begin execution.

A nice touch is the IF ERR conditional. Also notice the QUE key…




SR-60 Hardware



The SR-60 case bottom is cast aluminum. Vis-

ible here are the prin-ter, display board, and

the card reader and

power supply. The

actual electronics

are underneath

the keyboard.



The rear view gives us a better look at the power supply. Note the ribbon cable under the blue capacitor leading to a DB25 port on the rear of the calculator. TI calls this the “AUX” port, and the manual mentions accessories such as an electric typewriter and cassette drive.



This oblique view of the mainboard shows the two sets of stacked memory chips (near the center of the image) and the stacked ROM chips at the lower right. All chips except the ROMs and the CPU are socketed. This is all PMOS circuitry and is very static sensitive!



Since these chips are upside-down in the calculator, they tend to work their way out of the sockets. The first thing you should do when you get an SR-60 is open it up (with static precautions) and do a “chip press.”



Delicate, unkeyed, laminated plug-in cables: they’re used for the printer, card reader, and display. Most have started delaminating. I use a Sharpie to mark the side of the cable and the matching side of the socket.



TMC0501 4-bit CPU

• 16 digit precision (13 mantissa, 2 exponent, 1 sign & overflow bits)

• Contains keyboard and display drivers

• Requires at least one TMC0582 SCOM

• 28 pin DIP package, PMOS technology

• This CPU was used in many TI handhelds from 1974 through 1982



TMC0582 SCOM

• 2,500 13-bit(!) words of storage

• Sixteen 16-digit constants

• Two SCOMs are stacked in the SR-60

• 28 pin DIP package



TMC0599 RAM

• 5 chips total (lower two chips are stacked)

• 1,920 bits per chip for 1,200 bytes total

• Each chip holds 240 program steps or 30 data registers

• 16 pin DIP package



Memory Expansion

• Two slots accept boards with 8 additional TMC0599 chips (one 3 chip board and one 5 chip board)

• Thirteen total chips (SR-60A) equals 3,120 bytes of memory

• The white edge connector is for an additional memory board, but I’ve never seen or heard of one



Connectors

From top, proceeding clockwise: • Keyboard • Display • Card Reader • Aux • Printer



Programs and data are stored on magnetic cards that are dimensionally identical to the “long” cards used by the HP 9810 and 9820 calculators. The only difference is the write-protect punch out area on the HP cards. Each side of the card can hold 480 program steps or the contents of 60 data registers. A program may span multiple cards.



Programming the SR-60



• The SR-60 is a keystroke programmable calculator with limited alpha capabilities.

• No keystrokes are merged. However, the leading zero on memory register and program addresses may be omitted if the next instruction is non-numeric.

• The display shows key mnemonics rather than key codes.



Program editing is easy with the STEP, BSTEP, INSRT ,and DLETE keys. Numeric branch addresses are not adjusted automatically. However, the SR-60 does build a “jump table” of labels when you switch out of LEARN mode, so there’s really no reason to use numeric branches except for indirect SUBR and indirect GO TO instructions.



There are only three conditional branches. Their meaning may be inverted by preceding them with the 2nd key, i.e. “2nd IF POS” means “If negative”. The SR-60 does not have the “T” test register used in the TI-59, so if you want to see if a quantity is equal to “X”, subtract it from X and test for zero. The special sequence “2nd GO TO” decrements the quantity in register 0 and branches to the following label if it’s not zero.



The SR-60 supports 10 flags (0-9) and 12 levels of subroutines.



The IND key can be used with memory register operations STORE, RECALL, SUM, PROD, and EXCH. It can also be used with GO TO and SUBR to branch to a numeric address specified in a memory register.



The QUE key pauses the running program and displays the contents of the alpha register. The four labels following the QUE statement represent the code that will be jumped to if the YES, NO, NOT APPLY, and NOT KNOWN keys are pressed, respectively. The first program location after the fourth label will be jumped to when the ENTER key is pressed.



Memory is allocated between program steps and memory registers. In the SR-60A, the power-on state is 1920 program steps and 100 memory registers as shown above. To change the allocation, enter the number of desired registers divided by 10 and press 2nd X<->K. To see the current allocation, enter 0 and press 2nd X<->K.



So…let’s try a small program! We’ll generate the cubes of the integers 1 through 9 and store each in a separate memory register (i.e. the cube of 9 will be stored in register 9). Then we’ll compare the time it takes to run with similar programs on the HP 9810 and 9815 calculators.



0000 LBL

0001 e1

0002 9

0003 STO

0004 0

0005 LBL

0006 e2

0007 RCL

0008 0

0009 X

0010 RCL

0011 0

0012 X

0013 RCL

0014 0

0015 =

0016 IND

0017 STO

0018 0

0019 II

0020 GTO

0021 e2

0022 ALF

0023 D

0024 O

0025 N

0026 E

0027 ALF

0028 PRT

0029 RTN

Step 19 is the symbol for the “2nd” key, which when used in conjunction with GO TO acts as a “decrement and skip on 0” instruction for the quantity in register 0. The SR-60A completes this very simple program in about 7 seconds. Let’s try the same program on a 9815.

First, the SR-60A…



The HP 9815A is probably HP’s closest equivalent to the SR-60A, although it did cost about twice as much as a SR-60A when it came out. Interestingly, it uses a Motorola 6800 CPU, which is of course much more powerful than the TI’s little 4-bit processor.

0000 LBL

---- A

0002 1

0003 STO A

0004 9

0005 STO F

0006 FOR A->F

0007 RCL A

0008 3

0009 Y^X

0010 STO I A

0012 NEXT A

0013 STOP

You’ll notice that we used the expo- nentiation operator here, because the HP implementation produces integer results with integer arguments, while the SR-60 does not.

Running time: about 1.5 seconds.



0000 9

0001 X->()

0002 0

0003 0

0004 0

0005 X<-()

0006 0

0007 0

0008 0

0009 UP

0010 x

0011 x

0012 Y->()

0013 IND

0014 0

0015 0

0016 0

0017 1

0018 X->()

0019 -

0020 0

0021 0

0022 0

0023 X<-()

0024 0

0025 0

0026 0

0027 UP

0028 0

0029 X=Y?

0030 0

0031 0

0032 3

0033 9

0034 GTO

0035 0

0036 0

0037 0

0038 5

0039 END

The 1972-era 9810A, with what we might politely call a “very limited instruction set” and “weird early RPN implementation”, runs this program in about ½ second. It’s kind of amazing the Motorola 6800-equipped 9815 is slower… But the SR-60 is really slow! Let’s try another test…



TI SR-60AHP 9810A

HP 9815A

344

12453

25913

For all three calculators, I wrote a program that simply added 1 in a loop and looked at the result after 60 seconds. The 9810A and 9815A are 36 and 75 times faster, respectively, than the SR-60A.



Pros and Cons + Cheaper than equivalent HP Products.

+ Better program editing. + Full alphanumeric display. + Easier to set up for non-technical users. + Easy to repair gummy wheel on card reader. - Slow. Really slow. Glacially slow. - Delicate like butterfly. - Constructed entirely of unavailable custom T.I. chips. - Clumsy conditionals. - No broad collector base, schematics, etc. You’re on your own!



Credits “If I have written a decent presentation on the SR-60, it’s because I stole a lot of

information from various web sites.”

• Datamath.org and Joerg Woener: Personal help from Joerg, and chip specifications on his site.

• Oldcalculatormuseum.com: Rick Bensene is not afraid to dig into his systems!

• www.rskey.org: Viktor Toth’s site has a lot of good information.



SR-60 manuals are available at the Computer History Museum web site: http://www.computerhistory.org/collections/accession/102712699

texas instruments sr-60a - pahhc

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