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Article #625583Re: PDP 11/40 system manual
From: Questor
Date: Thu, 16 Aug 2018 08:42
Date: Thu, 16 Aug 2018 08:42
21 lines
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2857 bytes
dOn 14 Aug 2018 02:26:22 GMT, Charlie Gibbs <cgibbs@kltpzyxm.invalid> wrote: >On 2018-08-13, Questor <usenet@only.tnx> wrote: > >> One amusing pastime is to list *all* the different instructions that can >> be used to zero an accumulator... > >If your program counter, instruction register, and data registers are in >low-order memory, there are a lot of fun ways to code a one-instruction >loop. Decrementing the program counter by the length of the instruction >is just the beginning. Or you can decrement the program counter by twice >the length of the instruction and make your program run backwards. Most of the ways to zero an accumulator on the PDP-10 aren't loops, although there are a couple. Depending the contents of the register, they may take a while. (grin) The PDP-10 PC isn't stored in a general purpose register. However, its sixteen accumulators *are* mapped to the first sixteen memory locations, thus specific register-to-register instructions aren't needed. This flexibility, coupled with the orthogonal instruction set, results in more than two dozen instructions that will zero a register.
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X-Received: by 2002:adf:d4ca:: with SMTP id w10-v6mr2512234wrk.32.1534408901312; Thu, 16 Aug 2018 01:41:41 -0700 (PDT) X-BeenThere: alt.folklore.computers@googlegroups.com Received: by 2002:a1c:f00a:: with SMTP id a10-v6ls887491wmb.12.canary-gmail; Thu, 16 Aug 2018 01:41:40 -0700 (PDT) X-Received: by 2002:a1c:a00e:: with SMTP id j14-v6mr2256117wme.24.1534408900739; Thu, 16 Aug 2018 01:41:40 -0700 (PDT) MIME-Version: 1.0 Path: mbox-mo1.pugleaf.net!a22-v6ni8206wmg.0!nntp.google.com!goblin1!goblin2!goblin.stu.neva.ru!newsfeed.xs4all.nl!newsfeed9.news.xs4all.nl!85.12.16.70.MISMATCH!peer03.ams1!peer.ams1.xlned.com!news.xlned.com!peer03.am4!peer.am4.highwinds-media.com!peer01.iad!feed-me.highwinds-media.com!news.highwinds-media.com!post01.iad!fx12.iad.POSTED!not-for-mail From: usenet@only.tnx (Questor) Newsgroups: alt.folklore.computers Subject: Re: PDP 11/40 system manual Organization: random access Reply-To: usenet@only.tnx Message-ID: <5b7538c3.17012402@news.dslextreme.com> References: <21aaeee8-c41a-4442-a4eb-ea6a29b1e4f1@googlegroups.com> <0001HW.211B94B1040CADA5700004B5B2CF@news.giganews.com> <mdd7ekzl6pr.fsf@panix5.panix.com> <pki8ae$ca0$1@dont-email.me> <mddh8k2vyfh.fsf@panix5.panix.com> <pkl609$smf$1@dont-email.me> <38c09876-c7ce-4e49-9a08-e0f3cb7a8cbd@googlegroups.com> <y2a600gfvsx.fsf@offog.org> <5b7139cf.12146686@news.dslextreme.com> <pkteke228n8@news2.newsguy.com> X-Newsreader: Forte Free Agent 1.21/32.243 Lines: 22 X-Complaints-To: abu...@dslextreme.com NNTP-Posting-Date: Thu, 16 Aug 2018 08:41:40 UTC Date: Thu, 16 Aug 2018 08:42:06 GMT X-Received-Bytes: 2137 X-Received-Body-CRC: 1099745434 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit