1. Computer Architectures M
Memory Systems
Computer Architectures M

2. EPROM memories EPROM CE* OE* 128K  8 Cell M/bit i Di
Non volatile read-only memories 1
VPP
VCC 32
Capacities: two’s multiples: 32K, 64K, 128K, 256K……
PGM* 2
A16 31 NC 3
A15 30
Access time: ns
A14 4
A12 29 A7
A13 5 28 Ai
CE*
OE* Di
Tce
Tacc
Toe A6 A8 6 27 A5 A9 7 26
A11 8 A4 25
OE* 9 A3 24 A2
A10 10 23 11 A1
CE* 22 12 A0 D7 21 D6 13 D0 20 14 D1 D5 19 D4 15 D2 18
CE*
OE* Di
Cell M/bit i
Tri-state driver
GND D3 16 17
128K  8

3. Read Cycle Write Cycle RAM memories(SRAM) RAM 128K  8 Ai CE* Tce ToeNC
VCC 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 Ai
CE*
OE*
I/Oi
Tce
Tacc
Toe
(Out)
Read
Cycle 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
A16
A15
A14 NC
A12
WE* A7
A13 A6 A8 A5 A9 A4
A11 A3
OE* A2
A10 A1
CE* Ai
CE*
WE*
I/Oi
Taw
Twp
(In)
Tds
Write
Cycle A0
I/O7
I/O0
I/O6
I/O1
I/O5
I/O2
I/O4
GND
I/O3
128K  8
Volatiles memories, readable and writable
Capacity four’s multiples: 8K, 32K, 128K, 512K……
Access time: 5-40 ns
DRAM: 1 transistor per bit, higher capacity, less speed

4. 2n  N => 2n cells each of N bits
WR RD
Data bit
RAM cell D E C O R
2n  N => 2n cells each of N bits
Tri-state driver j
C Qi D
Cell Address: “j”

5. Decoder and Decoder matrix
C D “column decode”
(AND => associative property) A B
“row decode”

11. Register File (1 read-port, 1 write-port)C O R 1
M-1
EN* n
Read_Address
Write_Address
RD*
WR* N
Write_Data
Read_Data CK
D[0..N-1]
WE*
OE*
O[0..N-1] R0 R1
RM-1
N.B. :
M=2n
A memory device is a register file

12. Memories with 2K bytes
Any memory (and in particular memories with 8-bit parallelism – the only we will address), with 2k cells, has internally a k-variables decoder with E enable (negative true) input (this means that when E = 1 none of the outputs of the decoder is active) which selects one of the memory bytes. The memory interface has therefore the following signals
Address bits ( An….A0) which select the addressed byte (if E enabled)
Data bits (D7….D0)
At least one chip select (CS*) (called also “chip enable” (CE* - asterisk means «negative true») which is the enable of the decoder. If CS* is inactive (=1) it means that no byte of this memory (of this «chip») is addressed. CS* is used to selected a memory device when multiple devices are present
A memory bank (device) is «aligned» if its lowest address within the entire memory system is located at an address multiple of 2k (a 4 cells device is aligned if its two LSBs address are 0 – multiple of 4 -, a 64K cells device if its 16 LSBs are 0 etc.)
A Read Command (RD*) which enables the data onto the bus. Normally there is also an Output Enable (OE*) signal. The addressed byte of the memory is output only if CS*=RD*=OE*=0
If the memory is a RAM (read/write memory) another signal is present: write command WR* or WE* which allows to store bus data into the selected memory byte. Obiously this can occur only if CS*=RD*=OE*=0
Needless to say RD* and WR* are mutually exclusive
In a system there are normally multiple memory devices in order to implement memory systems bigger that a single device. Multiple devices are therefore needed, each one implementing a portion of the entire memory

13. An example: a 32 Kbytes memory system made with 8K devices
32 Kbytes correspond to a 15 bit address
Device selection
32K 8K 14 13 12
Devices internal address
Memory device implementing a memory system portion
0000
1FFF 8K 8K 8K
CS* = (A14  A13*)*
In this case 8K 0K
Memory space

14. 1MB address space (20 bit address 0-19) - 8 bit parallelism memory 64K bit ROM devices 256K memory bank – Addresses FFFF
FFFFF
0000
FFFF
64K
40000
4FFFF
50000
5FFFF
60000
6FFFF
70000
7FFFF B0 B1 B2 B3
512K
7FFFF
40000
256K
CS0 = A19* A18 A17* A16*
CS1 = A19* A18 A17* A16
CS2 = A19* A18 A17 A16*
CS3 = A19* A18 A17 A16
00000 14

15. Memory systems with parallelism > 8 An example: a 16 bit bus
memories internal address
Memories physical address = Logic address / 2 i 8 8
Chip pin A0 -> AD1 bus
A1 -> AD2 bus
……………………….. h 7 7
Word(4) -> Byteh(2) & Bytel(2) => 2 read
Logic
Physical
(f,e)
(f )
(e ) g 6 6
For each bus there must be a ByteEnable*
BE0* for bus7-0 e BE1* for bus15-8 f l 5 5 l e l 4 i 4
What about a word at address 7 (not aligned)???? d h 3 g 3
Word(7) -> Byteh(i) & Bytel(h) => 4/3 read
Logic
Physical
(i,h)
(i )
(h ) c f 2 e 2 b d 1 c 1
Two memory accesses!!!! a b a
The physical memories must be always coupled!
For instance 2 x 8K = 16 K !
Logic
memory
bit 15 8 7
Physical
memory
High BUS
Low BUS 15

16. Memory systems with parallelism > 8 An example: a 16 bit bus
mov al, even_byte_address ; transfer one byte at even address => one bus cycle 8 bit =>BE0*
mov al, odd_byte_address ; transfer one byte at odd address => one bus cycle 8 bit => BE1*
mov ax, even_word_address ; transfer one word at even address => one bus cycle 16 bit => BE0* and BE!*
mov ax, odd_word_address ; transfer one word at odd address => two 8 bit cycles => BE1* and then BE0* 16

17. MEMORIES in a 16 BIT SYSTEM (I.E. 8086)
The routing of byte high external to byte low internal is implemented within the microprocessor chip
Physical memories
Microprocessor Ri
MUX
BE1* BE0*
Word
Odd addresses
Even addresses
High Byte (odd addr.)
Low Byte(even addr.)
No transfer
A0 of the processor not generated (instead BE0* and BE1*)
A1 of the processor connected to chip pin A0
A2 of the processor connected to chip pin A1
etc. etc.

18. EPROM internal addresses
Memory systems with parallelism > 8 A 16 bit bus in a 1MB memory (19 to 0 addresses)
Physical
memory
High BUS
Low BUS
64K 7
bit 7
0000h
FFFFh
EPROM internal addresses
2 x 64K = 128K
EPROM1
BE1*
EPROM0
BE0*
FFFFFh
128K
128K
(5H=0101B ; 4H=0100B)
5FFFFh
128K
40000h
CSEPROM1= A19*  A18  A17*  BE1
CSEPROM0= A19*  A18  A17*  BE0
In the square the bank selection
CS here in positive true form
128K
00000h
Logic
memory
The decoding is performed as if a 8-bit memory were used.
Devices (a couple!) (each one half size of the bank) are used
and selected by BE0 e BE1

19. (logic even addresses)
Memory systems with parallelism > 8 A 16 bit bus in a 1MB memory (19 to 0 addresses)
HIGH BUS
(logic odd addresses)
Eprom pin
Bus Pin
EPROM1
BE1* - 64K
FFFF
FFFE
FFFD
FFFC
0003
0002
0001
0000
EPROM internal addresses
Odd mP addresses
LOW BUS
(logic even addresses)
0 Eprom Pin
0 Bus Pin 7
EPROM0
BE0* - 64K
FFFF
FFFE
FFFD
FFFC
0003
0002
0001
0000
EPROM internal addresses
Even mP addresses
Logic Memory
5FFFH
5FFFE
5FFFD
5FFFC
5FFFB
40005
40004
40003
40002
40001
40000
128K
Logic memory addresses

20. Memory systems with parallelism > 8 A 32 bit bus
Physical
Memory
Logic
Memory i 8 8 h 7 7
Always 4
coupled devices
Internal memories
physical address is the
processor address/4 g 6 6 f 5 5 e 4 4 d 3 c 2 l i 2 b h g f e 1 1 a d c b a
bit 31 24 23 16 15 8 7
BUS 3
BE3*
BUS 2
BE2*
BUS 1
BE1*
BUS 0
BE0*

21. N.B. Processor A0 and A1 are not generated
32 BIT bus memories
BE3* BE2* BE1* BE0*
Word 32 bit
Half word low
Half word high
byte 0-7
byte 15-8
etc.
N.B. Processor A0 and A1 are not generated
(instead BE0*, BE1*, BE2*, BE3* are generated)
Processor A2connected to memories A0
Processor A3connected to memories A1
etc. etc.

22. EPROM internal addresses
32 BIT bus memories (NB the symbol ! before a logic variable is equivalent to asterisk and means negation)
Memory bank selection
CSEPROM3= !A31  A30  !A29  !A28  !A27  !A26  !A25  !A24 
!A23  !A22  !A21  BE3
CSEPROM2= !A31  A30  !A29  !A28  !A27  !A26  !A25  !A24 
!A23  !A22  !A21  BE2
CSEPROM1= !A31  A30  !A29  !A28  !A27  !A26  !A25  !A24 
!A23  !A22  !A21  BE1
CSEPROM0= !A31  A30  !A29  !A28  !A27  !A26  !A25  !A24 
!A23  !A22  !A21  BE0
CS as
Positive true form
Physical Memory
BUS 3
512K 24 31
00000h
7FFFFh
EPROM internal addresses
EPROM3
BE3* 16 23
EPROM2
BE2* 8 15
EPROM1
BE1* 7
EPROM0
BE0*
BUS 2
BUS 1
BUS0
BUS
selection
Aligned memory
FFFFFFFFh
2MB
401FFFFFh
2MB h
In the selected bank
eleven high address bit
are identical
2MB h
Logic Memory
4 Memories x 512K= 2MB

23. Generated by the processor
32 BIT bus memories
FFFFFFFFh
2MB
Physical Memory
BUS 3 - D24-31 mP
BE3*
512K
7FFFFh
Generated by the processor
instead of A1 and A0
EPROM3
00000h
BUS 2 - D23-16
401FFFFFh
2MB
BE2*
512K
7FFFFh h
EPROM2
00000h
BUS1 - D15-8
BE1*
512K
7FFFFh
EPROM1
00000h
BUS 0 - D7-0
2MB h
BE0*
512K
7FFFFh
EPROM0
Logic Memory
00000h
Internal
addresses

24. Consecutive addresses data are on different devices
32 BIT bus memories
Physical Memory
(as really implemented)
2MB
EPROM3
401FFFFFh
7FFFFh
512K
physical addreses
of the devices
EPROM2
7FFFFh
512K
EPROM1
7FFFFh
512K
EPROM0
abcdefgh x h
00001h
7FFFFh
512K d
00000h g
00001h c
00000h
------ h e f
00001h h d b
00000h h c h b
Consecutive addresses data
are on different devices e
00001h h a a
00000h
Logic Memory
(as seen by the programmer)
Byte x at logical address abcdefgh is located at physical address
abcdefgh/4 of EPROM i where i is the rest of the division

25. Exercise
A 256K memory RAM (32 bit parallelism) bank starting at address H in a 4GB memory space using the minimum number of devices. No 128K and greater size RAM available
What is the address range?
What RAM devices can be used ?
What are the logic functions of the CE*
Does the address parallelism influence the CE*?
What if the data parallelism were 64 bit?

26. Exercise
A 256K memory RAM (32 bit parallelism) starting at address (aligned) in a 4GB memory space . Address range FFFF. Devices: 8X32 K RAM devices (64K RAM do not exist!!!!)
Therefore two banks of 128K : the first implements the range to 8401FFFF and the other the range to 8403FFFF. The 32K memory chips use internally the addresses A14-A0 which are connected to bus addresses BA16-BA2 . Notice that bus address BA17 separates the two banks
First bank
CSRAM00=(BA31BA30!BA29!BA28!BA27!BA26 .…BA18!BA17!)BE0
CSRAM01=(BA31BA30!BA29!BA28!BA27!BA26 ….BA18!BA17!)BE1
CSRAM02=(BA31BA30!BA29!BA28!BA27!BA26 ….BA18!BA17!)BE2
CSRAM03=(BA31BA30!BA29!BA28!BA27!BA26 ….BA18!BA17!)BE3
Second bank
CSRAM10=(BA31BA30!BA29!BA28!BA27!BA26 ….BA18!BA17) BE0
CSRAM11=(BA31BA30!BA29!BA28!BA27!BA26 ….BA18!BA17) BE1
CSRAM12=(BA31BA30!BA29!BA28!BA27!BA26 ….BA18!BA17) BE2
CSRAM13=(BA31BA30!BA29!BA28!BA27!BA26 ….BA18!BA17) BE3
If the parallelism of the memory were 64 bit the 8 CS (CSRAM00..CSRAM07) would NOT be affected by BA17: BE7-BE0 instead would play its role. The 8 devices would implement the entire memory bank and memory chips addresses A14-A0 would be connected to bus addresses BA17-BA3 !! It is the parallelism which changes not the address range!!!