标签: rom

单片机就是个小计算机，大计算机少不了的数据存储系统，单片机一样有，而且往往和CPU集成在一起，更加显得小巧灵活。 直到90年代初，国内容易得到的单片机就是8031：不带存储器的芯片，要想工作，还必须外加RAM和ROM，单片机成了3片机...... 现在不同了，大的小的又是51，又是AVR又是STC，还有什么430，PIC等等，都各说各的好，可是谁也不敢说“我不要存储器”。 单片机的数据存储手段 程序存储器ROM 程序存储器里面存放的是单片机的灵魂：工作程序。 小的可能只有1KB，最多只能装1024条8位数据，因为实际指令还有许多2字节，3字节指令，所以它还装不下1024条指令。大的也有128KB的。这些8位数据，要么在工厂里做模子光刻进去，要么一次性的烧写进去。 业余或开发，最多也就是用编程器这么一个特殊工具，把调试成功的机器码装载进去，或者像AVR单片机那样自己花几块钱做一条下载线，把电脑里这些东西灌进去（或许是AVR最吸引人之处）。 它一旦进驻电脑的程序存储器中，除了借助上述装置便不能自由改写，在单片机运行时，只是从其中读出指令或固定的数据，所以给程序存储器一个“只读存储器”的别名，简写为ROM，包括用编程器写紫外线擦除内容的EPROM、用电擦除的EEPROM和现在新兴的FLASH ROM。 一次性写入的ROM，仅用于电路和程序固定的批量产品中，实际工作起来，都是一样的。 为了定位ROM中的数据，每个8位存储单元都有一个固定的“地址”，通常用16进制数表示。例如，对于一个所谓4K的ROM，地址从0000H到0FFFH（即从0000，0001...4095），单片机运行时从哪个地址取数据，完全由程序本身决定，并不要我们干预。 记住，给单片机一通电，它经过一个短暂的复位过程，立即转向ROM的最低地址0000H，在这里面放置的往往是一条“跳转”指令，它从这里一步跳到另一个地址：程序的真正起始地址，例如51机的0080H。 ROM是程序存储器，除了指令外，还包括运行程序必须的某些固定数据，例如：数据表。假如，我们要求在单片机的接口上输出00H到FFH（255）按正弦半波变化的数值，每秒10000次。如果硬要它按照公式一个个计算，对于它来说未免力不从心。可是我们可以把预先计算好的数值存入ROM中，到时候直接取出不是好多了？ 又如一个重要的应用：大家一定见过不少单片机的东西上面都有数码显示，那些个数字其实就是用单片机的口线控制数码管的字段电极电位。这些字形也是存放在ROM中的字模表，各个字模和0-9的数字（机器内当然是0000-0101二进制数）对应起来。常见的共阳极7段数码管，必须在阳极加正电，7个阴极都是地电位，才能显示数字"8"，数字8对应的显示字码值是二进制数“10000000“（那个1对应的是小数点，高电位不让它显示）。 数据存储器RAM 这是个可以随时存取数据的一块存储器，也就是可以读（取）也可以写（存）的存储器，简称RAM。 现在的单片机里面使用的RAM，属于静态RAM或SRAM，这个和电脑用的内存条有所不同。只要你把数据写入SRAM后，不断电或者不清除掉，这个数据就一直保存在那里。电脑用的是动态RAM，要不断给它加刷新脉冲才能保存数据。 因为单片机处理的信息量比电脑小很多，所以它带的RAM也比较少：从完全不带、带128、256、...1K、2K，到4K，比ROM少多了。 因为实际上RAM只是作为数据临时存放的地方，除非进行图像处理需要存放大量的数据外。一般对于执行较简单任务的单片机，有这么多也够用，如果实在不够用也只能采取外加SRAM如6116、6264等等来扩展。 为了对RAM单元存取8位二进制数，当然也得和ROM一样用“地址”来标示它的具体位置。假如某单片机有1K（1024）RAM，它的地址也是从0000到1024，或16进制数的0000H到03FFH。可见，和ROM的地址是一样的。 会不会混淆不清？ 不会，因为读ROM是由单片机的程序指针或转移指令或查表指令进行，而这些指令是不会进入RAM区的；读写RAM是另外的数据传送指令，也不会进入ROM区。这点也是和电脑不同之处，后者程序和数据都在内存条里面，地址不同，如果窜位了就会造成不可预见后果。单片机的这种存储器结构也称为哈佛结构。 RAM在单片机里的用途 RAM在单片机里的用途，主要是存放临时数据。 例如用单片机测温，每秒测1次，显示1分钟的平均值（1分钟更新一次）： 我们先通过传感器、放大电路、A/D转换，把温度这个模拟量转变为成比例的二进制数，然后每秒钟1次把数字量通过输入口顺序存入到单片机的RAM中，然后对他们进行两两求和再平均的计算，最后的数值显示出来，然后把这60个存储单元统统写0清除旧数据，下次又是如此循环进行。 结语 另外在单片机里面还有若干寄存器，数量不多但是作用很大，除了暂存数据，还可以交换、加工、传递等等，以及随时记录单片机当前处于什么状态，输入输出口也是作为特殊功能的寄存器存在，具体各有不同，就不是随便说说可以搞清楚的，要看有关书籍了。 - END - 关于造物工场 造物工场立足金百泽超过20年柔性电子制造服务优势，聚焦产品方案和电子工程的设计服务，提供从创意到制造、PCB/PCBA/BOM/元器件等一站式硬件服务。

  憋了很久，到了今天终于可以写写锤子ROM了。   因为老罗的锤子ROM终于发布了，然后看完网上的发布会，提心吊胆生怕一觉醒来世界被颠覆的我终于放下心来。   终于可以光明正大名正言顺的喷一喷他了。   其实今天锤子ROM出来，网上肯定会呈现三种声音，这也在意料之中：   支持？中立？还是反对？   跟你们不一样，你们是因为手机才知道老罗，而我很早就知道老罗，我给你们讲讲老罗这个人。那个时候他没有干牛博网，没有学会发微博，没有拍电影，没有做手机，没有拿曾轶可当偶像，没有砸西门子，没有跟方舟子对掐，没有后来这么多乱七八糟的事......   那个时候的老罗给我们的印象是一段段录音里的段子，这个颇有传奇经历的英语老师浑身上下散发着理想主义的细菌......，这从一句句经典语录中可以看出：   比如：彪悍的人生不需要解释！！！   比如 ：有的鸟来到世间,是为了做它该做的事,而不是专门躲弹子儿的！！！   比如：不被嘲笑的梦想是不值得实现的！！！   这三句话都被罗粉翻来覆去说烂了，看懂了这三句话，你就可以理解老罗从过去到今天的行为轨迹了！   所以对于那些之前被老罗骂土鳖，其实心里幸灾乐祸，但表面上还要故作有风度，甚至还要祝福老罗加油一路走好的手机业同行们，我只想说一句话：你们累不累？想嘲笑就笑出来，表里如一点好么！你们如果不嘲笑他，那他的梦想还有什么值得实现的？你们嘲笑他其实就是成全他啊！是佛心来的啊！！！   如果你们要看的是我对锤子ROM的具体分析，那就很抱歉了，一个ROM一定要亲身上手体验其流畅度和顺畅度才行，没量产使用的东西叫我怎么评价？但我相信这个ROM至少不会比刷机精灵里80%的ROM难用。我今天要说说锤子ROM最大的杀手锏，也就是理想主义这回事。   我们一般小时候的理想就是长大之后要干什么，比如你是要当科学家，总统，还是奥运冠军？   再大一点知道以前自己多么幼稚了，理想就直接一点，变成是要当大款还是伙夫？   直到有一天，理想变成了一场场演讲，变成畅销书的标题，变成一种宗教，于是你发现理想还能变成了一门生意。简单点说，就是一个你看上去各方面条件看起来都不如自己的人登上讲台，先说说革命家史，将自己以前怎么吃苦受罪最后发财致富成功的故事。   本来这是挺好一个事，众屌丝乐呵乐呵，然后结束的时候狠狠怒吼一声“高富帅宁有种乎”，皆大欢喜！   可关键是人家还要颠覆一下你的三观，把你过去十几二十年受过的教育推倒重来一遍。   比如：彪悍的人生不需要解释！！！   比如 ：有的鸟来到世间,是为了做它该做的事,而不是专门躲弹子儿的！！！   比如：不被嘲笑的梦想是不值得实现的！！！   -----------   还比如“吹牛”这个事情，这个在北方叫吹牛逼。我奶奶评价喜欢吹牛的人叫“半桶水”，以前我觉得这样的人大家应该都是讨厌的。后来我进入社会，发现不少吹牛的人要比不吹牛的人混得要好。   再后来我进入手机行业，发现吹牛也能成为一种工作，业内人士亲切的称之为“营销”。再后来......秒杀、横扫、土鳖、颠覆......吹牛成为了一门艺术，并被众人膜拜。   可以毫不夸张的说，在这一方面，老罗已经超越了所有国产手机，进入了另一个境界。因为老罗早已吹牛为荣，以不吹牛为耻了，从精神层面就已经超越你们了。   比如中国广大“土鳖企业”文化里广泛认可的“低调做人，高调做事”，就被老罗嗤之以鼻，他表示自己一定是“高调做人，高调做事”，我把高调理解为吹牛，不知道恰不恰当。   在老罗的多年熏陶下，老罗的铁杆粉丝早就对你们中国人各种陋习、价值观和传统文化中的糟粕嗤之以鼻了，他们今天一定很委屈，你们这些人在老罗微博留言里冷嘲热讽的时候，他们的心情一定好像玉米当年看到网友黑春春一样。因为他们觉得老罗的行为和言论是在正常不过了。   当理想成为一门生意，当吹牛成为一种竞争力，当你的粉丝与你形成同样一种价值观时，产品要卖出去只是时间问题了。   所以，如果要评价乔布斯在中国的三大传人：雷布斯和黄章各学到其一部分功夫，纷纷回去勤学苦练，最终小有所成。而老罗学到的是其最精深的武学理念，但是根基不稳，功力没练出来学了一招半式就开始出来闯荡江湖。   最后，对于广大的“土鳖”国产手机厂商们，希望你们学习或借鉴的是老罗身上精神层面的东西，而不是回头叫UI的产品经理抄一下锤子ROM的功能和界面。   这种做法比贩卖理想主义更糟糕哦！

憋了很久，到了今天终于可以写写锤子ROM了。   因为老罗的锤子ROM终于发布了，然后看完网上的发布会，提心吊胆生怕一觉醒来世界被颠覆的我终于放下心来。   终于可以光明正大名正言顺的喷一喷他了。   其实今天锤子ROM出来，网上肯定会呈现三种声音，这也在意料之中： 支持，中立，反对   跟你们不一样，你们是因为手机才知道老罗，而我很早就知道老罗，我给你们讲讲老罗这个人。那个时候他没有干牛博网，没有学会发微博，没有拍电影，没有做手机，没有拿曾轶可当偶像，没有砸西门子，没有跟方舟子对掐，没有后来这么多乱七八糟的事......   那个时候的老罗给我们的印象是一段段录音里的段子，这个颇有传奇经历的英语老师浑身上下散发着理想主义的细菌......，这从一句句经典语录中可以看出：   比如：彪悍的人生不需要解释！！！ 比如 ：有的鸟来到世间,是为了做它该做的事,而不是专门躲*子儿的！！！ 比如：不被嘲笑的梦想是不值得实现的！！！   这三句话都被罗粉翻来覆去说烂了，看懂了这三句话，你就可以理解老罗从过去到今天的行为轨迹了！   所以对于那些之前被老罗骂土鳖，其实心里幸灾乐祸，但表面上还要故作有风度，甚至还要祝福老罗加油一路走好的手机业同行们，我只想说一句话：你们累不累？想嘲笑就笑出来，表里如一点好么！你们如果不嘲笑他，那他的梦想还有什么值得实现的？你们嘲笑他其实就是成全他啊！是佛心来的啊！！！   如果你们要看的是我对锤子ROM的具体分析，那就很抱歉了，一个ROM一定要亲身上手体验其流畅度和顺畅度才行，没量产使用的东西叫我怎么评价？但我相信这个ROM至少不会比刷机精灵里80%的ROM难用。我今天要说说锤子ROM最大的杀手锏，也就是理想主义这回事。   我们一般小时候的理想就是长大之后要干什么，比如你是要当科学家，总统，还是奥运冠军？   再大一点知道以前自己多么幼稚了，理想就直接一点，变成是要当大款还是伙夫？ 直到有一天，理想变成了一场场演讲，变成畅销书的标题，变成一种宗教，于是你发现理想还能变成了一门生意。简单点说，就是一个你看上去各方面条件看起来都不如自己的人登上讲台，先说说革命家史，将自己以前怎么吃苦受罪最后发财致富成功的故事。   本来这是挺好一个事，众屌丝乐呵乐呵，然后结束的时候狠狠怒吼一声“高富帅宁有种乎”，皆大欢喜！   可关键是人家还要颠覆一下你的三观，把你过去十几二十年受过的教育推倒重来一遍。   比如：彪悍的人生不需要解释！！！ 比如 ：有的鸟来到世间,是为了做它该做的事,而不是专门躲*子儿的！！！ 比如：不被嘲笑的梦想是不值得实现的！！！ ------   还比如“吹牛”这个事情，这个在北方叫吹牛逼。我奶奶评价喜欢吹牛的人叫“半桶水”，以前我觉得这样的人大家应该都是讨厌的。后来我进入社会，发现不少吹牛的人要比不吹牛的人混得要好。   再后来我进入手机行业，发现吹牛也能成为一种工作，业内人士亲切的称之为“营销”。再后来......秒杀、横扫、土鳖、颠覆......吹牛成为了一门艺术，并被众人膜拜。 可以毫不夸张的说，在这一方面，老罗已经超越了所有国产手机，进入了另一个境界。因为老罗早已吹牛为荣，以不吹牛为耻了，从精神层面就已经超越你们了。   比如中国广大“土鳖企业”文化里广泛认可的“低调做人，高调做事”，就被老罗嗤之以鼻，他表示自己一定是“高调做人，高调做事”，我把高调理解为吹牛，不知道恰不恰当。   在老罗的多年熏陶下，老罗的铁杆粉丝早就对你们中国人各种陋习、价值观和传统文化中的糟粕嗤之以鼻了，他们今天一定很委屈，你们这些人在老罗微博留言里冷嘲热讽的时候，他们的心情一定好像玉米当年看到网友黑春春一样。因为他们觉得老罗的行为和言论是在正常不过了。   当理想成为一门生意，当吹牛成为一种竞争力，当你的粉丝与你形成同样一种价值观时，产品要卖出去只是时间问题了。   所以，如果要评价乔布斯在中国的三大传人：雷布斯和黄章各学到其一部分功夫，纷纷回去勤学苦练，最终小有所成。而老罗学到的是其最精深的武学理念，但是根基不稳，功力没练出来学了一招半式就开始出来闯荡江湖。   最后，对于广大的“土鳖”国产手机厂商们，希望你们学习或借鉴的是老罗身上精神层面的东西，而不是回头叫UI的产品经理抄一下锤子ROM的功能和界面。   这种做法比贩卖理想主义更糟糕哦！

Debugging involved loading the tape of the object code and then using the monitor to run or step through the program. At least it allowed breakpoints and even a one line assembler. Some of the more sophisticated monitors allowed addressing by name rather than absolute address, but I can't recall how this one worked. Once again, corrections in the short term were implemented using patches so as to avoid having to re-assemble. The same techniques of GOTOs and leaving gaps between subroutines applied here. Once the development was over, the object code was loaded into a PROM programmer and then the EPROM was inserted in to the target hardware. Next was the eternal challenge – how do you know that the system is working or – more importantly – why it is not working? Some people wrote their own monitors to address this, but I quickly became a confirmed believer in In-Circuit Emulators. As you can imagine some of these tapes were quite long. It was possible to get the tape in fan-fold format, but I never manage to find a supplier. Organising the length of paper tape could be quite a challenge. They could form a roll 5" or 6" in diameter. Reading them would result in many feet of tape spewed out over the floor. Rewinding them was not only tedious but could also lead to damage of the tape. My solution (although not my original idea) was to wind them on to a plastic bobbin derived from a sewing cotton reel. My mom was a sewer and there were many "empties". I see they are still available. I would cut a slot and feed the tape into it. Then I had to find a method to wind it on. I acquired a manual grinding wheel (see photo below), removed the grindstone, and wound tape around the shaft to increase the diameter. I then wedged the bobbin onto the shaft and although it was a two handed operation, rolling the tape became a breeze.   My grinding wheel was very useful for winding paper tapes   Most of the CP/M computers at this time (around 1979) were designed to work with a teletype input, which quickly morphed into "glass teletypes" as dumb terminals were called. In the middle of our desktop computer development, Lear Siegler (one of the glass teletype manufacturers) brought out a desktop system that was a clone of the DEC (the largest minicomputer manufacturer of the day) PDP12. We figured there was no way we could compete and so I was left rudderless. It did not matter that DEC successfully sued Lear Siegler and their product never made it to market. I found my way into some industrial design and decided to revert to Intel, largely because of the quality of the support, both hardware and personnel, of their distributor in South Africa. I broke down and financed an Intel MDS236 development system with ICE for the 8085 and 8048 families. The equipment cost more than my house! The paper tape approach had been replaced by 3 8" floppy drives- 1 single density (720KB) and 2 double density drives (1.2KB). I also had a high level language: PL/M. It was now possible to develop software in modules and use libraries. Although the processes were similar (three-pass assembly), they were transparent to the user and there was mostly enough disc space to do this, although sometimes you had to shuffle floppies. It mainly supported Intel products, although there was a plug in ICE for a Z80 (see photo below).   I got a project designing a calorimeter and, for cost reasons, the customer opted for an 8080. I could produce my code on the development system since 8080 and 8085 code was identical, but I could not debug since I did not have (and couldn't afford) and new ICE. I managed to get a used Intel development tool called aµScope which was essentially a reduced feature emulator in an attaché case (see photo below). The user interface was a bit clumsy (especially as I never received a user manual), but still usable.   I also acquired an Osborne 1 for the express purpose of producing data manuals (using Wordstar ) so that I would look professional. I also ordered Supercalc , which was my first introduction to the world of spreadsheets. ( Supercalc was for CP/M-based computers; Visicalc was for Apple machines.) The Osborne 1 was a "luggable" computer and had a 5" screen that was like a magnifying glass view of your document. You could see about 24 characters (of an 80 character wide document) and 10 lines at a time. Storage was limited to two 360KB 5¼ inch floppy disks, one of which had the application you were running. Changing floppies was not a simple task of opening the drive latch, removing one, and inserting another disc. On CP/M machines there was some initialisation required every time disc was inserted, all of which further complicated mass storage. We've come a long way! The IBM PC finally became accepted as the industry standard about 1983 (in SA at least) and I started moving towards using it for documentation and PC layout. More than that though, Intel started accepting it as the development base for all their hardware and introduced the ICE5100 emulator for the 8051 hosted on a PC via an RS232 connection. Intel even created emulators to run all the existing software compilers, assemblers, editors under PC-DOS. By 1986 the development approach was not much different to what it is today, with the major exception of the user interface. Unlike the single chip microcomputers that we use today, back then the microprocessor had to connect to RAM, ROM and peripherals externally. That meant there were up to 8 data lines, 16 address lines, and 3 control signals (27 lines) snaking their way around a PCB. The probability for a manufacturing fault increased dramatically and Hewlett Packard believed they had a technique to aid debugging when a product failed test in manufacturing. They created an instrument called a Signature Analyzer (see photo below) to capitalise on the idea. It also provided much amusement when seen by the uninitiated who assumed it applied to one's John Hancock.   In circuits with repetitive waveforms, diagnostic manuals had pictures of the waveforms identified with nodes and the settings that produced these waveforms. Of course microprocessor busses are non-repetitive and it is quite an art to debug them. HP's idea was to provide some "waveform" at each node to prove that the system was working. The concept was to force the micro to run a set of instructions that would repeat a bit pattern through a particular node. This pattern is fed into a shift register (in the Signature Analyzer) with some feedback loops similar to CRC calculation to generate a 16 bit signature that is displayed as a 4-digit hexadecimal word on the instrument. That could only be done when the basic system was working. To start up there had to be some method of opening the data bus and forcing the micro to execute a single instruction over and over to allow the exercise of the address bus and ROM read signal. This was fairly easy in Intel processors because the NOP instruction was 00hex and so all that was needed was an 8 way DIP switch to open the bus and 8 diodes connected in a common cathode arrangement with a switch to ground. You could then establish a signature on each address line and EPROM data output, and slowly enable the memories etc. from there.  

The beauty of the nameless sequence is that whenever the number of wires double we only have to add one new test pattern. That is, 8 wires require 4 test patterns, 16 wires require 5 test patterns, 32 wires require 6 test patterns, and so on. Thus, as the number of wires increase, so does the efficiency of the "nameless" sequence in comparison to the walking ones sequence. Note that if you're using the "nameless" sequence and the number of wires is not equal to a power of two (2, 4, 8, 16, 32, 64, ...), then you can add some imaginary wires to create the sequence and discard them at the end. For example, if you have 5, 6, or 7 wires, you would add enough pseudo-wires to bring the total number of wires up to 8, write the test sequence based on 8 wires, and then drop the pseudo wires. The "nameless" sequence unmasked! After I had first mentioned my "nameless" sequence in an article in EDN magazine many years ago, I received a jolly pleasant letter from Mr. Norman Megill, Vice President of Engineering at Production Services Corporation, Belmont, MA. Mr. Megill pointed out that my "nameless" sequence should more properly be referred to as the Modified Counting Sequence Algorithm as per a 1989 IEEE paper: N. Jarwala and C.W. Yau, "A New Framework for Analyzing Test Generation and Diagnosis Algorithms for Wiring Interconnects," Proceedings, IEEE International Test Conference, 1989, pp. 63-70 Mr. Megill went on to note that, to the best of his knowledge, this algorithm was first documented by himself in a 1979 paper: N.D. Megill, "Techniques for Reducing Pattern Counts for Functional Testing," Digest of Papers, IEEE Test Conference 1979, pp. 90-94 In fact my discussions on the nameless sequence prompted a slew of emails from readers who had independently come up with the same thing. Furthermore, several readers noted a trick they used to generate a variation on the nameless sequence, which simply involves writing down a standard binary count sequence, commencing at 1, proceeding up to the number of wires you wish to test, and then "rotating" the results. For example, assuming that we wish to test 10 wires called a through j for stuck-ats, bridges, and open faults, we would commence by writing the binary values for 1 to 10 as illustrated in Figure 3(a).   Figure 3: Generating a variation of the nameless sequence.   Once we've generated the binary count, we conceptually "rotate" the table 90 degrees clockwise (or anti-clockwise if you are so-inclined) to create the final test sequence as illustrated in Figure 3(b). This scheme has an advantage over my nameless sequence in that it results in one less test for any number of wires except 2 n (I tell you, I learn something new every day). Actually testing the device Using the "nameless" sequence (or similar) to generate addresses, we would first write corresponding "nameless-sequence-based" data values into each "nameless" location and then read these values back again. This would ensure that we had access to the device and that there were no short, open, or bridging faults on the address or data busses. The next step would be to write functional tests that verify the internals of each memory device, but these techniques are a tad more complex and will therefore be left as topics for future columns. And the answer is... And so, returning to my original tale of woe, how could it be that my tests passed when there wasn't even any memory in the cabinet? Arrggghhh! It was all due to parasitic capacitances on the data and address busses. Whatever 010101... (or similar) value that I wrote to the bus persisted long enough for me to read it back again. I cannot tell you how silly I felt when I discovered my mistake, but that's how we learn... the real trick is to not make the same mistake more than once (grin).