Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!wuarchive!ukma!rsg1.er.usgs.gov!rsg1.er.usgs.gov!stevev From: stevev@greylady.uoregon.edu (Steve VanDevender) Newsgroups: comp.sys.handhelds Subject: Re: The First (?) HP Calculator (long) Message-ID: Date: 8 Jun 91 16:18:18 GMT References: <1991Jun6.153021.10025@ll.mit.edu> Sender: news@rsg1.er.usgs.gov Organization: University of Oregon Chemistry Stores Lines: 31 In-Reply-To: wjc@llex.ll.mit.edu's message of 6 Jun 91 15: 30:21 GMT Thank you for the informative posting on the HP 9100A. I was lucky enough to pick up one of these for free and it is over on the table right now chunking away on a somewhat trivial program (and has been for months). One minor correction: The 9100A has a mantissa of 12 BCD digits although no more than 10 are shown on the display. Each BCD digit is stored in a 6-bit word, so there are two extra bits which are used as special flags. Bit 4 is used to indicate a negative digit and bit 5 suppresses display of that digit (which is how certain things like integer add, subtract, and multiply maintain display precision for results). When you store a floating-point number in a register and examine it in program mode, you can see the floating-point format. A number stored in register 0 has the ten most significant mantissa digits stored in the order least significant to most significant going from 0.0 to 0.9. Bit 4 of 0.9 is the mantissa sign (negative if set); in some cases bit 4 of all mantissa nibbles in a negative number is set. 0.a and 0.b have the exponent with least significant digit in 0.a. Bit 4 of 0.b is set if the exponent is negative. 0.c and 0.d will two additional mantissa digits which cannot be displayed (except by subtracting out the 10 most significant digits of the mantissa). -- Steve VanDevender stevev@greylady.uoregon.edu "Bipedalism--an unrecognized disease affecting over 99% of the population. Symptoms include lack of traffic sense, slow rate of travel, and the classic, easily recognized behavior known as walking."