Shop OBEX P1 Docs P2 Docs Learn Events
How many address lines does it take to address 128K ? — Parallax Forums

How many address lines does it take to address 128K ?

Kaos KiddKaos Kidd Posts: 614
edited 2006-06-23 16:06 in General Discussion
Ok.
I have this nifty little Maxim DS1245W chip...· 128K X 8 bit sram
It's got A0 ~ A16 (17 pins) for addressing...
Now I'm somewhat confused...
Last time I checked, I needed 16 pins...
So what is the extra address pin for?
The data sheets reads "A0 ~ A16 - Address Inputs"
ideas or pointers... please???

Heres the data sheet:· http://pdfserv.maxim-ic.com/en/ds/DS1245W.pdf




▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Just tossing my two bits worth into the bit bucket


KK
·

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2006-06-22 19:39
    128K = 2 ^ 17, so it needs 17 address pins.
    64K = 2 ^ 16, the largest memory addressable with 2 bytes
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2006-06-22 19:42
    128,000 Bytes = % 1 1111 0100 0000 0000 (17 bits, A16 - A0)


    127,999 Bytes = % 1 1111 0011 1111 1111 (17 bits, A16 - A0)

    [noparse][[/noparse]because it is byte 0 - byte 127,999 actually]

    Post Edited (PJ Allen) : 6/22/2006 8:07:54 PM GMT
  • SSteveSSteve Posts: 808
    edited 2006-06-23 03:04
    I would bet that 128k in this case is not 128 * 1000, but 128 * 1024 (2^7 * 2^10 = 2^17). k=1000 is used in hard drive sizes, but I've never seen it used in memory sizes. So 128k = 131072 and 128k-1 = 1_1111_1111_1111_1111.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    OS-X: because making Unix user-friendly was easier than debugging Windows

    links:
    My band's website
    Our album on the iTunes Music Store
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2006-06-23 03:24
    Well, the data sheet says 1,024k-bits (128k x 8)

    But, I know what you mean, like "1MB" of memory; it's not 1,000,000, it's really 1,024,000 (I believe), more than 1 million.
  • SSteveSSteve Posts: 808
    edited 2006-06-23 05:45
    All this 1k=1000 vs 1k=1024 stuff comes from the fact that 10^3 is nearly equal to 2^10. So "k" morphed into "one thousand" in the vernacular. So 128k dollars is $128,000 but 128k of RAM is 131,072 bytes.

    1MB is 1024 * 1024, or 1,048,576. Unless you are a hard drive manufacturer in which case 1MB = 1,000,000 which lets you claim greater capacity.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    OS-X: because making Unix user-friendly was easier than debugging Windows

    links:
    My band's website
    Our album on the iTunes Music Store
  • Kaos KiddKaos Kidd Posts: 614
    edited 2006-06-23 16:06
    Thanks all... Got it...
    I was trying to duplicate the hardware in Digital Works 3, and ran into some confusion:
    THe software has ram up to 16K...
    So I WAS going to use the CE and the rest of the lines to "build" up to the 128K...
    but, there are 4 lines (0~13) = 16K, 14~17 would be used as chip enable select, but led to 16 16K devices, not the anticipated 8 16k devices.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Just tossing my two bits worth into the bit bucket


    KK
    ·
Sign In or Register to comment.