piclist 1995\12\01\114544a >
Thread: 512 Kbyte of memory
www.piclist.com/techref/mems.htm?key=memory
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face BY : Tommy Brown email (remove spam text)



On Thu, 2 Nov 1995, PETE KLAMMER said:

Subject: : 32Kbyte NV FRAMs?
> > From: Don McKenzie <KILLspamdonmckSTOPspamspam@spam@tbsa.com.au>
> > Subject: Re: 512 KByte of memory: EASIEST WAY!!!
> >
> > He said 512 Kilobytes!!
-------------clip---------clip-----------------------------
> Well, for adequate density/capacity, for one, eh?  Sorry if I got anyone's
> hopes up.
-------------clip---------clip-----------------------------

Hi, I have been following your threads on interfacing 512K x 8 memory
to PICs.

I have Dallas Semiconductor's 11 page data sheet for their 3 wire to
bytewide bus interface 1280.ps (370k).

The chip has the following features:

* Adapts JEDEC bytewide memory to a 3-wire serial port

* Supports 512k bytes of memory

* 80-pin version provides arbitration mechanisms for dual port operation

* CMOS circuitry for battery backup and battery operate applications

* Cyclic redundancy check monitors serial transmission for error

* Available in 44/80 pin quad flat pack for high density requirements

A short description from data sheet page 1, is as follows:

The DS1280 adds a 3-wire serial port to a bytewide static RAM, yet
maintains the existing bytewide port.  Memory capacity of up to 512K x 8
bytes can be addressed directly.  Arbitration between the serial and
bytewide port is accomplished by handshaking or using predictable idle
time as an access window.  The serial protocol requires a 6 byte protocol
to set up memory transfers.  Cyclic redundancy check circuitry is included
to monitor serial data transmission error.

The 3-wire serial port will correctly read and write any byte wide static
RAM with an effective access time of 200ns.

The serial interface uses bi-directional data pin (DQ), unlike other
three/four wire interfaces which have separate Data In and Data Out pins.

Data pins description follows:
___
RST             RESET FOR SERIAL PORT

Clk             CLOCK INPUT FOR SERIAL PORT

DQ              DATA INPUT/OUTPUT FOR SERIAL PORT

DQOE            SERIAL PORT ACTIVE OUTPUT       *AVAILABLE ONLY ON 44 PIN
VERSION

DQE             SERIAL PORT ACTIVE OUTPUT       *AVAILABLE ONLY ON 80 PIN
VERSION
___
CEB             SYSTEM BUS ENABLE               *AVAILABLE ONLY ON 80 PIN
VERSION
___
OEB             SYSTEM BUS READ ENABLE          *AVAILABLE ONLY ON 80 PIN
VERSION
___
WEB             SYSTEM BUS WRITE ENABLE         *AVAILABLE ONLY ON 80 PIN
VERSION

A0B-A18B        SYSTEM ADDRESS BUS              *AVAILABLE ONLY ON 80 PIN
VERSION

D0B-D7B         SYSTEM DATA BUS                 *AVAILABLE ONLY ON 80 PIN
VERSION
___
CER             RAM CHIP ENABLE
___
WER             RAM WRITE ENABLE
___
OER             RAM OUTPUT ENABLE

A0R-A18R        RAM ADDRESS BUS

D0R-D7R         RAM DATA BUS

GND             GROUND

Vcc             5 VOLTS
----------------------------------------------------------------------------
------
As you can see it is able to both access NV static ram, and the 80 pin
version can allow access to system bus of another cpu.

It appears to be good choice to expand an existing PIC design, which may
have a serial interface already implemented, but other I/O pins commited
to other tasks.

It makes at most a single chip solution to expand a PIC or any 8 bit cpu
to access additional ram.

Dallas also has chips that combine the features for cpu/ram reset for power
down or brown-out protection, with a real time clock that runs on 3V lithium
power cells when your cpu/ram is in sleep mode.

Dallas also have plug-in non/volatile read write cartridge with size up
to 512K x 8 byte, which is ideal for data-logging.  It can be inserted or
removed by non-technical persons.  It has manual read/write enable switch
in cartridge, and has hot swap feature built-in.  It is DS1217M, data sheet
is 1217M.PS (postscript).

You can retrieve full data sheets as well as application notes for these
and other chips at:

ftp.dalsemi.com/pub/datasheets/

regards

********************************************************************************
* Tom Brown
E-Mail:KILLspamtombrownspamindo.net.id  *
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<9512011645.AA06130@MIT.EDU>

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