Interface Design Memory Modules

University of Tehran 1

Interface DesignMemory Modules

Omid Fatemi([email protected])


Outline

• Memory variations

• The memory cell


Processor Timing Diagramfor any memory read machine cycle

IOR

IOW

MEMR

MEMW

___

____

_____

______

AddressBus

Data Bus

T1 T2 T3

CLOCK

memory address

datain


Processor Timing Diagramfor any memory write machine cycle

IOR

IOW

MEMR

MEMW

___

____

_____

______

AddressBus

Data Bus

T1 T2 T3

CLOCK

memory address

data out


Memory Terms

• Capacity – Kbit, Mbit, Gbit

• Organization– Address lines– Data lines

• Speed / Timing– Access time

• Write ability– ROM– RAM


ROM Variations

• Mask Rom

• PROM – OTP

• EPROM – UV_EPROM

• EEPROM

• Flash memory


RAM Variations

• SRAM

• DRAM

• NV-RAM– SRAM – CMOS

– Internal lithium battery

– Control circuitry to monitor Vcc


Memories in General

• Computers have mostly RAM

• ROM (or equivalent) needed to boot

• ROM is in same class as Programmable Logic Devices (PLDs), in which are also FPGAs

– Lots of memories in these devices


Simple View of RAM

• Of some word size n• Some capacity 2k

• k bits of address line• Maybe have read line• Have a write line• Have a CS (chip select)


1K x 16 memory

• Variety of sizes– From 1-bit wide

• Issue is no. of pins

• Memory size specified in bytes– This would be 2KB memory

• 10 address lines and 16 data lines


Writing

• Sequence of steps– Setup address lines– Setup data lines– Activate write line (maybe a pos edge)– Usually latch on the next edge


Reading

• Steps– Setup address lines– Activate read line– Data available after specified amt of time


Chip Select

• Usually a line to enable the chip


Writing


Reading


Minimum Mode

MEMORY

D7 - D0 Q7 - Q0

OELE 74LS373

D7 - D0 Q7 - Q0

OELE 74LS3738088

AD7 - AD0

A15 - A8

A19/S6 - A16/S3

DENDT / R

IO / M

RD

WR

ALE

D7 - D4 Q7 - Q4

OELE 74LS373

D3 - D0 Q3 - Q0

GND

GND

GND

D7 - D0A7 - A0 B7 - B0

EDIR 74LS245

A7 - A0A15 - A8A19 - A16

RD

WR


Minimum Mode

MEMORY

D7 - D0

A19 - A0

RD

WR

SimplifiedDrawing of

8088 MinimumMode

D7 - D0

A19 - A0

MEMR

MEMW

When Memory is selected?


Minimum Mode

MEMORY

D7 - D0

A19 - A0

RD

WR

SimplifiedDrawing of

8088 MinimumMode

D7 - D0

A19 - A0

MEMR

MEMWCS

220 bytes or 1MB


What are the memory locations of a 1MB (220 bytes) Memory?

A19 to A0

(HEX)

AAAA11119876

AAAA11115432

AAAA11981000

AAAA7654

AAAA3210

00000 0000 0000 0000 0000 0000

FFFFF 1111 1111 1111 1111 1111

Example: 34FD0 0011 0100 11111 1101 0000


Interfacing a 1MB Memory to the 8088 Microprocessor

230000000001

100001000110002100031000410005100061000710008

95

::

45982739428807F48A

::

20020200212002220023

FFFFDFFFFEFFFFF

29127D13

192536

::

::

::

::A19

A0:

D7

D0:

RD

WR

A19

A0:

D7

D0:

MEMR

MEMW

XXXX

BP

ESDSSS

CXBXAX

XXXXXXXX

XXXX2000

000000233F1C

FCA1

SP

DX

XXXXCS

SI

XXXX

XXXXIP

XXXXDI

CS


Instead of Interfacing 1MB, what will happen if you interface a 512KB Memory?


What are the memory locations of a 512KB (219 bytes) Memory?

A18 to A0

(HEX)

AAAA11119876

AAAA11115432

AAAA11981000

AAAA7654

AAAA3210

00000 0000 0000 0000 0000 0000

7FFFF 0111 1111 1111 1111 1111


Interfacing a 512KB Memory to the 8088 Microprocessor

A18

A0:

D7

D0:

MEMR

MEMWXXXX

BP

ESDSSS

CXBXAX

XXXXXXXX

XXXX2000

000000233F1C

FCA1

SP

DX

XXXXCS

SI

XXXX

XXXXIP

XXXXDI

230000000001 95

::

20020200212002220023

7FFFD7FFFE7FFFF

29127D13

192536

::

::

::

A18

A0:

D7

D0:

RD

WR

CS

A19What do we do with A19?


What if you want to read physical address A0023?

A18

A0:

D7

D0:

MEMR

MEMWXXXX

BP

ESDSSS

CXBXAX

XXXXXXXX

XXXXA000

000000233F1C

FCA1

SP

DX

XXXXCS

SI

XXXX

XXXXIP

XXXXDI

230000000001 95

::

20020200212002220023

7FFFD7FFFE7FFFF

29127D13

192536

::

::

::

A18

A0:

D7

D0:

RD

WR

CS

A19


What if you want to read physical address A0023?

A19 to A0

(HEX)

AAAA11119876

AAAA11115432

AAAA11981000

AAAA7654

AAAA3210

A0023 1010 0000 0000 0010 0011

A19 is not connected to the memory so even if the 8088 microprocessor outputs a logic “1”, the memory cannot “see” this.


What if you want to read physical address 20023?

A18 to A0

(HEX)

AAAA11119876

AAAA11115432

AAAA11981000

AAAA7654

AAAA3210

20023 0010 0000 0000 0010 0011

For memory it is the same as previous one.


Interfacing two 512KB Memory to the 8088 Microprocessor

A18

A0:

D7

D0:

MEMRMEMW

XXXX

BP

ESDSSS

CXBXAX

XXXXXXXX

XXXX2000

000000233F1C

FCA1

SP

DX

XXXXCS

SI

XXXX

XXXXIP

XXXXDI

A19

230000000001 95

:20020200212002220023

7FFFD7FFFE7FFFF

29127D13

192536

:

:

:

A18

A0:

D7

D0:

RDWRCS

970000000001 D4

:20020200212002220023

7FFFD7FFFE7FFFF

A3924533

2C9812

:

:

:

A18

A0:

D7

D0:

RDWRCS



• Problem: Bus Conflict. The two memory chips will provide data at the same time when microprocessor performs a memory read.

• Solution: Use address line A19 as an “arbiter”. If A19 outputs a logic “1” the upper memory is enabled (and the lower memory is disabled) and vice-versa.



A18

A0:

D7

D0:

MEMRMEMW

XXXX

BP

ESDSSS

CXBXAX

XXXXXXXX

XXXX2000

000000233F1C

FCA1

SP

DX

XXXXCS

SI

XXXX

XXXXIP

XXXXDI

A19

230000000001 95

:20020200212002220023

7FFFD7FFFE7FFFF

29127D13

192536

:

:

:

A18

A0:

D7

D0:

RDWRCS

970000000001 D4

:20020200212002220023

7FFFD7FFFE7FFFF

A3924533

2C9812

:

:

:

A18

A0:

D7

D0:

RDWRCS


What are the memory locations of two consecutive 512KB (219 bytes) Memory?

A19 to A0

(HEX)

AAAA11119876

AAAA11115432

AAAA11981000

AAAA7654

AAAA3210

00000 0000 0000 0000 0000 0000

7FFFF 0111 1111 1111 1111 1111

80000 1000 0000 0000 0000 0000

FFFFF 1111 1111 1111 1111 1111


A18

A0:

D7

D0:

MEMRMEMW

XXXX

BP

ESDSSS

CXBXAX

XXXXXXXX

XXXX2000

000000233F1C

FCA1

SP

DX

XXXXCS

SI

XXXX

XXXXIP

XXXXDI

A19

230000000001 95

:20020200212002220023

7FFFD7FFFE7FFFF

29127D13

192536

:

:

:

A18

A0:

D7

D0:

RDWRCS

970000000001 D4

:20020200212002220023

7FFFD7FFFE7FFFF

A3924533

2C9812

:

:

:

A18

A0:

D7

D0:

RDWRCS


When the P outputs an address between 80000 to FFFFF, this memory is selected

When the P outputs an address between 00000 to 7FFFF, this memory is selected



A18

A0:

D7

D0:

MEMRMEMW

XXXX

BP

ESDSSS

CXBXAX

XXXXXXXX

XXXX2000

000000233F1C

FCA1

SP

DX

XXXXCS

SI

XXXX

XXXXIP

XXXXDI

A19

230000000001 95

:20020200212002220023

7FFFD7FFFE7FFFF

29127D13

192536

:

:

:

A18

A0:

D7

D0:

RDWRCS

970000000001 D4

:20020200212002220023

7FFFD7FFFE7FFFF

A3924533

2C9812

:

:

:

A18

A0:

D7

D0:

RDWRCS



A18

A0:

D7

D0:

MEMRMEMW

XXXX

BP

ESDSSS

CXBXAX

XXXXXXXX

XXXX2000

000000233F1C

FCA1

SP

DX

XXXXCS

SI

XXXX

XXXXIP

XXXXDI

A19

230000000001 95

:20020200212002220023

7FFFD7FFFE7FFFF

29127D13

192536

:

:

:

A18

A0:

D7

D0:

RDWRCS

970000000001 D4

:20020200212002220023

7FFFD7FFFE7FFFF

A3924533

2C9812

:

:

:

A18

A0:

D7

D0:

RDWRCS

A18

A0:

D7

D0:

RDWR

A19


A18

A0:

D7

D0:

MEMRMEMW

XXXX

BP

ESDSSS

CXBXAX

XXXXXXXX

XXXX2000

000000233F1C

FCA1

SP

DX

XXXXCS

SI

XXXX

XXXXIP

XXXXDI

A19

230000000001 95

:20020200212002220023

7FFFD7FFFE7FFFF

29127D13

192536

:

:

:

A18

A0:

D7

D0:

RDWRCS

970000000001 D4

:20020200212002220023

7FFFD7FFFE7FFFF

A3924533

2C9812

:

:

:

A18

A0:

D7

D0:

RDWRCS

What if we remove the lower memory?


What if we remove the lower memory?

A18

A0:

D7

D0:

MEMRMEMW

XXXX

BP

ESDSSS

CXBXAX

XXXXXXXX

XXXX2000

000000233F1C

FCA1

SP

DX

XXXXCS

SI

XXXX

XXXXIP

XXXXDI

A19

230000000001 95

:20020200212002220023

7FFFD7FFFE7FFFF

29127D13

192536

:

:

:

A18

A0:

D7

D0:

RDWRCSWhen the P outputs

an address between 80000 to FFFFF, this memory is selected

When the P outputs an address between 00000 to 7FFFF, no memory chip is selected !


Full and Partial Decoding

• Full Decoding– When all of the “useful” address lines are connected the

memory/device to perform selection

• Partial Decoding– When some of the “useful” address lines are connected

the memory/device to perform selection– Using this type of decoding results into roll-over

addresses


Full Decoding

A18

A0:

D7

D0:

MEMRMEMW

XXXX

BP

ESDSSS

CXBXAX

XXXXXXXX

XXXX2000

000000233F1C

FCA1

SP

DX

XXXXCS

SI

XXXX

XXXXIP

XXXXDI

A19

230000000001 95

:20020200212002220023

7FFFD7FFFE7FFFF

29127D13

192536

:

:

:

A18

A0:

D7

D0:

RDWRCS


Full Decoding

A19 to A0

(HEX)

AAAA11119876

AAAA11115432

AAAA11981000

AAAA7654

AAAA3210

80000 1000 0000 0000 0000 0000

FFFFF 1111 1111 1111 1111 1111

A19 should be a logic “1” for the memory chip to be enabled


Full Decoding

A19 to A0

(HEX)

AAAA11119876

AAAA11115432

AAAA11981000

AAAA7654

AAAA3210

00000 0000 0000 0000 0000 0000

7FFFF 0111 1111 1111 1111 1111

Therefore if the microprocessor outputs an address between 00000 to 7FFFF, whose A19 is a logic “0”, the memory chip will not be selected


Partial Decoding

A18

A0:

D7

D0:

MEMR

MEMWXXXX

BP

ESDSSS

CXBXAX

XXXXXXXX

XXXX2000

000000233F1C

FCA1

SP

DX

XXXXCS

SI

XXXX

XXXXIP

XXXXDI

230000000001 95

::

20020200212002220023

7FFFD7FFFE7FFFF

29127D13

192536

::

::

::

A18

A0:

D7

D0:

RD

WR

CS

A19


Partial Decoding

A19 to A0

(HEX)

AAAA11119876

AAAA11115432

AAAA11981000

AAAA7654

AAAA3210

00000 0000 0000 0000 0000 0000

7FFFF 0111 1111 1111 1111 1111

80000 1000 0000 0000 0000 0000

FFFFF 1111 1111 1111 1111 1111The value of A19 is INSIGNIFICANT to the memory chip, therefore A19 has no bearing whether the memory chip will be enabled or not


Partial Decoding

A19 to A0

(HEX)

AAAA11119876

AAAA11115432

AAAA11981000

AAAA7654

AAAA3210

00000 0000 0000 0000 0000 0000

7FFFF 0111 1111 1111 1111 1111

80000 1000 0000 0000 0000 0000

FFFFF 1111 1111 1111 1111 1111

ACTUAL ADDRESS


Partial Decoding

A19 to A0

(HEX)

AAAA11119876

AAAA11115432

AAAA11981000

AAAA7654

AAAA3210

00000 0000 0000 0000 0000 0000

7FFFF 0111 1111 1111 1111 1111

80000 1000 0000 0000 0000 0000

FFFFF 1111 1111 1111 1111 1111

ACTUAL ADDRESS


Interfacing two 512K Memory Chips to the 8088 Microprocessor

8088Minimum

Mode

A18

A0:

D7

D0:

MEMRMEMW

A19

512KB#2

A18

A0:

D7

D0:

RDWRCS

512KB#1

A18

A0:

D7

D0:

RDWRCS


Interfacing one 512K Memory Chips to the 8088 Microprocessor

8088Minimum

Mode

A18

A0:

D7

D0:

MEMRMEMW

A19

512KB

A18

A0:

D7

D0:

RDWRCS


Interfacing one 512K Memory Chips to the 8088 Microprocessor (version 2)

8088Minimum

Mode

A18

A0:

D7

D0:

MEMRMEMW

A19

512KB

A18

A0:

D7

D0:

RDWRCS


Interfacing one 512K Memory Chips to the 8088 Microprocessor (version 3)

8088Minimum

Mode

A18

A0:

D7

D0:

MEMRMEMW

A19

512KB

A18

A0:

D7

D0:

RDWRCS


Interfacing four 256K Memory Chips to the 8088 Microprocessor

8088Minimum

Mode

A17

A0:

D7

D0:

MEMRMEMW

A18

256KB#3

A17

A0:

D7

D0:

RDWR

CS

A19

256KB#2

A17

A0:

D7

D0:

RDWR

CS

256KB#1

A17

A0:

D7

D0:

RDWR

CS

256KB#4

A17

A0:

D7

D0:

RDWR

CS



8088Minimum

Mode

A17

A0:

D7

D0:

MEMRMEMW

A18

256KB#3

A17

A0:

D7

D0:

RDWR

CS

A19

256KB#2

A17

A0:

D7

D0:

RDWR

CS

256KB#1

A17

A0:

D7

D0:

RDWR

CS

256KB#4

A17

A0:

D7

D0:

RDWR

CS



8088Minimum

Mode

A17

A0:

D7

D0:

MEMRMEMW

A18

256KB#3

A17

A0:

D7

D0:

RDWR

CS

A19

256KB#2

A17

A0:

D7

D0:

RDWR

CS

256KB#1

A17

A0:

D7

D0:

RDWR

CS

256KB#4

A17

A0:

D7

D0:

RDWR

CS



8088Minimum

Mode

A17

A0:

D7

D0:

MEMRMEMW

A18

256KB#3

A17

A0:

D7

D0:

RDWR

CS

A19

256KB#2

A17

A0:

D7

D0:

RDWR

CS

256KB#1

A17

A0:

D7

D0:

RDWR

CS

256KB#4

A17

A0:

D7

D0:

RDWR

CSI1I0 O3

O2

O1

O0


Interfacing several 8K Memory Chips to the 8088 P

8088Minimum

Mode

A12

A0:

D7

D0:

MEMRMEMW

A13A14

8KB#2

A12

A0:

D7

D0:

RDWR

CS

8KB#1

A12

A0:

D7

D0:

RDWR

CS

8KB#?

A12

A0:

D7

D0:

RDWR

CS

A15A16A17A18A19

::


8088Minimum

Mode

A12

A0:

D7

D0:

MEMRMEMW

A13A14

8KB#2

A12

A0:

D7

D0:

RDWR

CS

8KB#1

A12

A0:

D7

D0:

RDWR

CS

8KB#128

A12

A0:

D7

D0:

RDWR

CS

A15A16A17A18A19

::

Interfacing 1288K Memory Chips to the 8088 P


8088Minimum

Mode

A12

A0:

D7

D0:

MEMRMEMW

A13A14

8KB#2

A12

A0:

D7

D0:

RDWR

CS

8KB#1

A12

A0:

D7

D0:

RDWR

CS

8KB#128

A12

A0:

D7

D0:

RDWR

CS

A15A16A17A18A19

::



Memory chip#__ is mapped to:

A19 to A0

(HEX)

AAAA11119876

AAAA11115432

AAAA11981000

AAAA7654

AAAA3210

----- ---- ---- ---- ---- ----

----- ---- ---- ---- ---- ----


Memory Chip

• 8K SRAM• to be specific:

– 8Kx8 bits SRAM

6264

A0A1A2A3A4A5A6A7A8A9A10A11A12

CS2

I/O0I/O 1I/O 2I/O 3I/O 4I/O 5I/O 6I/O 7

CS1

OEWE


6264 Block Diagram


6264 Function Table


Memory Chip

• 8K EPROM• to be specific:

– 8Kx8 bits EPROM

2764

A0A1A2A3A4A5A6A7A8A9A10A11A12

VPP

Q0Q1Q2Q3Q4Q5Q6Q7

C

GP


2764 Block Diagram

Chip enable

Output enable


Operating Modes


Programming 2764

• after each erasure for UV-EPROM):– all bits of the M2764A are in the “1" state.

• The only way to change a “0" to a ”1" is by ultraviolet light erasure.

• Programming mode when:– VPP input is at 12.5V– E and P are at TTL low.

• The data to the data output pins. • The levels required for the address and data

inputs are TTL.


8088Minimum

Mode

A12

A0:

D7

D0:

MEMRMEMW

A13A14

8KB#2

A12

A0:

D7

D0:

RDWR

CS

8KB#1

A12

A0:

D7

D0:

RDWR

CS

8KB#128

A12

A0:

D7

D0:

RDWR

CS

A15A16A17A18A19

::



When interfacing memory chips to a microprocessor, consider the following:

• TAVDV – address access time• TRLDV – read access time• TDVWH – memory setup time• TWHDX – data hold time• TWLWH – write pulse width

Refer to 8088 data manual


HM6264B Series Read Timing Diagram

tAA, tOE


HM6264B Series Write Timing Diagram

tDW, tDH, tWP


Timing Requirements for 6264 SRAM

• TAVDV = tAA

• TRLDV = tOE

• TDVWH = tDW

• TWHDX = tDH

• TWLWH = tWP


HM6264B Series Read TIMING REQUIREMENTS

HM6264B-8L HM6264B-10L Symbol Parameter Min Max Min Max Units

tRC Read cycle time 85 100 ns

tAA Address access time 85 100 ns

tCO1 Chip select access time (CS1’) 85 100 ns

tCO2 Chip select access time (CS2’) 85 100 ns

tOE Output enable to output valid 45 50 ns

tLZ1 Chip selection to output in low-Z (CS1) 10 10 ns

tLZ2 Chip selection to output in low-Z (CS2) 10 10 ns

tOLZ Output enable to output in low-Z 5 5 ns

tHZ1 Chip deselection in to output in high-Z (CS1’) 0 30 0 35 ns

tHZ2 Chip deselection in to output in high-Z (CS2’) 0 30 0 35 ns

tOHZ Output disable to output in high-Z 0 30 0 35 ns

tOH Output hold from address change 10 10 ns


HM6264B Series Write TIMING REQUIREMENTS

HM6264B-8L HM6264B-10L Symbol Parameter Min Max Min Max Units

tWC Write cycle time 85 100 ns

tCW Chip selection to end of write 75 80 ns

tAS Address setup time 0 0 ns

tAW Address valid to end of write 75 80 ns

tWP Write pulse width 55 60 ns

tWR Write recovery time 0 0

tWHZ WE’ to output in high-Z 0 30 0 35 ns

tDW Data to write time overlap 40 40 ns

tDH Data hold from write time 0 0 ns

tOW Output active from end of write 5 5 ns

tOHZ Output disable to output in high-Z 0 30 0 35 ns


Comparing Timing Requirements of 8088 (using 4 Mhz clock) and HM6264B-8L

8088 using 4MHz clk Timing Req. HM6264B-8L 610 ns TAVDV or tAA 85 ns 555 ns TRLDV or tOE 45 ns 400 ns TDVWH or tDW 40 ns 88 ns TWHDX or tDH 0 ns

440 ns TWLWH or tWP 55 ns


Timing Requirements for HM6264B-8L

• TAVDV = tAA = 85 ns• TRLDV = tOE = 45 ns• TDVWH = tDW = 40 ns• TWHDX = tDH = 0 ns• TWLWH = tWP = 55 ns


Can we interface a 2764 to the 8088 chip which uses a 4MHz clock?


M2764A Read Mode AC Characteristics

-3 -4 Symbol Alt Parameter Min Max Min Max Units

tAVQV tACC Address Valid to Output Valid 180 200 ns

tELQV tCE Chip Enable Low to Output Valid 180 200 ns

tGLQV tOE Output Enable Low to Output Valid 65 75 ns

tEHQZ tDF Chip Enable High to Ourput Hi-Z 0 55 0 55 ns

tGHQZ tDF Output Enable High to Output Hi-Z 0 55 0 55 ns

tAXQX tDH Address Transition to Output Transition 0 0 ns


M2764A Read Mode Timing Diagram


Timing Requirements for 2764 EPROM

• TAVDV = tAVQV

• TRLDV = tGLQV

• TDVWH = N/A • TWHDX = N/A• TWLWH = N/A


Timing Requirements for 2764 EPROM

• TAVDV = tAVQV = ?• TRLDV = tGLQV = ?• TDVWH = N/A• TWHDX = N/A • TWLWH = N/A


M2764A Read Mode AC Characteristics

-3 -4 Symbol Alt Parameter Min Max Min Max Units

tAVQV tACC Address Valid to Output Valid 180 200 ns

tELQV tCE Chip Enable Low to Output Valid 180 200 ns

tGLQV tOE Output Enable Low to Output Valid 65 75 ns

tEHQZ tDF Chip Enable High to Ourput Hi-Z 0 55 0 55 ns

tGHQZ tDF Output Enable High to Output Hi-Z 0 55 0 55 ns

tAXQX tDH Address Transition to Output Transition 0 0 ns


Timing Requirements for M2764A-3

• TAVDV = tAVQV = 180 ns• TRLDV = tGLQV = 65 ns• TDVWH = N/A• TWHDX = N/A • TWLWH = N/A


Comparing Timing Requirements of 8088 (using 4 Mhz clock) and M2764A-3

8088 using 4MHz clk Timing Req. HM6264B-8L 610 ns TAVDV or tAVQV 180 ns 555 ns TRLDV or tGLQV 65 ns


What if we need to interface a “slow” memory to the 8088?


Comparing Timing Requirements of 8088 (using 4 Mhz clock) and a certain “slow” memory chip

8088 using 4MHz clk Timing Req. memory chip 610 ns TAVDV or tAA 85 ns 555 ns TRLDV or tOE 45 ns 400 ns TDVWH or tDW 40 ns 88 ns TWHDX or tDH 0 ns

440 ns TWLWH or tWP 500 ns


8088Minimum

Mode

A12

A0:

D7

D0:

MEMRMEMW

A13A14

HM6264B-8L

A12

A0:

D7

D0:

OEWE

CS1 CS2

SLOWMEMORY

A12

A0:

D7

D0:

RDWR

CS

M2764A-3

A12

A0:

Q7

Q0:

G

C

A15A16A17A18A19

::

5V

READY


Recall:Write Pulse Width / Write-Time (TWLWH)

ALE

T1

CLOCK

T2 T3 T4

AD7 - AD0

A15 - A8

A19/S6 - A16/S3

DT/R __

IO/M __

_____

WR

DEN______

A19 - A0from 74LS373 to memory

A15 - A8

A19 - A16 S6 - S3

A19 - A0 from 74LS373

A7 - A0 D7 - D0 (to 74LS245)

D7 - D0from 74LS245 to memory

D7 - D0 (to memory)A7 - A0

TWLWH

2TCLCL


Write Pulse Width / Write-Time (TWLWH) w/ 1 wait state

ALE

T1

CLOCK

T2 T4

AD7 - AD0

A15 - A8

A19/S6 - A16/S3

READY

IO/M __

_____

WR

DEN______



TWLWH

A7 - A0 D7 - D0 (to memory)

A7 - A0 D7 - D0 (to 74LS245)

A15 - A8

A19 - A16 S6 - S3

A19 - A0 from 74LS373

DT/R __

TW T3


Comparing Timing Requirements of 8088 (using 4 Mhz clock) and a certain memory chip

8088 using 4MHz clk Timing Req. memory chip 610 ns TAVDV or tAA 85 ns 555 ns TRLDV or tOE 45 ns

400 ns + 250 ns TDVWH or tDW 40 ns 88 ns + 250 ns TWHDX or tDH 0 ns 440 ns + 250 ns TWLWH or tWP 500 ns

caused by 1 wait state during a memory write on the “slow” memory chip


How do we produce a wait state?

• By turning the READY input of the 8088 microprocessor to LOW


8088Minimum

Mode

A12

A0:

D7

D0:

MEMRMEMW

A13A14

HM6264B-8L

A12

A0:

D7

D0:

OEWE

CS1 CS2

SLOWMEMORY

A12

A0:

D7

D0:

RDWR

CS

M2764A-3

A12

A0:

Q7

Q0:

G

C

A15A16A17A18A19

::

5V

READY

University of Tehran 88Requirements for the READY input of the 8088

ALE

T1

CLOCK

T2 T4

AD7 - AD0

A15 - A8

A19/S6 - A16/S3

READY

IO/M __

_____WR

DEN______



30 ns(min)

A7 - A0 D7 - D0 (to memory)

A7 - A0 D7 - D0 (to 74LS245)

A15 - A8

A19 - A16 S6 - S3

A19 - A0 from 74LS373

DT/R __

TW T3

119 ns(min)

University of Tehran 89Requirements for the RDY of the 8284

T1

CLOCK

T2 T4

RDY1

35 ns(min)

TW T3

READY


Memory2 x m Bitn

m - Bit Data

n - Bit

Addressdecoder

Address

Memory - Global Organisation


Static vs Dynamic RAM

• SRAM vs DRAM

• DRAM stores charge in capacitor– Disappears over short period of time

– Must be refreshed

• SRAM easier to use– Faster

– More expensive per bit

– Smaller sizes


Structure of SRAM

• Control logic• One memory cell per bit

– Cell consists of one or more transistors– Not really a latch made of logic

• Logic equivalent


16 X 1 RAM

What is this?


Tri-State

• Have three states: H, L, and Hi-Z– High impedance– Behaves line no output connection if in Hi-Z state– Allows connecting multiple outputs


Multiplexed with Hi-Z

• Normal behavior is blue areaSmoke


Row/Column

• If RAM gets large, there is a large decoder• Also run into chip layout issues• Larger memories usually “2D” in a matrix

layout


16 X 1 as 4 X 4 Array

• Two decoders– Row– Column

• Address just broken up

• Not visible from outside


Change to 8 X 2 RAM

• Minor change in logic

• Also pinouts• Address 011 (for

example)


m - Bit DataColumn Address DecoderColumn selection

RowAddressDecoder

Memory cell

Quadratic

Memory Matrix

2 Lines (Bit Lines)n / 2

- Bit Column Addressn / 2

- Bitn / 2Row Address

n - Bit Address

2 Linesn / 2

(Word Lines)

m Level

W/E CS OE PGM

Control Logic

Memory - Internal Organisation


SRAM Performance

• Current ones have cycle times in low nanoseconds (say 2.5ns)

• Used as cache (typically offchip secondary cache)

• Sizes up to 8Mbit or so for fast chips• SRAMs:

– Asynchronous– Synchronous


Micron SRAMs

• SyncBurst

• ZBT

• QDR

• DDR (common IO)

• DDR (separate IO)

• Synchronous

• Control inputs are captured at clock edges


SRAM Categories

• SYNCBURST– Internal 2-bit burst counter– Appropriate for cache line size of four– Two bus master support (CPU and cache controller)– ADV# controls number of words– Not suited for more frequent bus turnaround applications

• ZBT (Zero Bus Turnaround)– Internal 2-bit burst counter– FLOW-Through ZBT

» One clock cycle delay» Less data latency and less frequency

– Pipelined ZBT» While data is delivered the memory array is free for the next

data access» Higher frequency


Pentium Cache System


SRAM QDR

• QDR (Quad Data Rate)– Low latency, higher frequency (network applications)– Less ASIC pin count– Separate read and write busses simultaneous read and

write– Clock pair (K,K#)


SRAM DDR

• DDR (common IO)– In cases like 16 read then 16 write QDR is half wasted– Common IO busses for input and output

• DDR (separate IO)– Hybrid of DDR and QDR

Documents

Interface Design Memory Modules