SMJ44C256 Datasheet, PDF (3/21 Pages) Texas Instruments – 262144 BY 4-BIT DYNAMIC RANDOM-ACCESS MEMORY

functional block diagram
SMJ44C256
262144 BY 4-BIT
DYNAMIC RANDOM-ACCESS MEMORY
SGMS034C – MAY 1989 – REVISED JUNE 1995
RAS CAS W G
Timing and Control
Row
Address
Buffers
(9)
256K Row 256K
Array Decode Array
A0
Sense Amplifiers
A1
A2
A3
A4
A5
Column
Address
Buffers
(9)
Column Decode
I/O
Buffers
4 of 8
Data
4
In
Reg
A6
A7
Selection
Data
Out
4
A8
Reg
4
Sense Amplifiers
256K Row 256K
Array Decode Array
DQ1–DQ4
operation
enhanced page mode
Page-mode operation allows faster memory access by keeping the same row address while selecting random
column addresses. The time for row-address setup and hold and address multiplex is eliminated. The maximum
number of columns that can be accessed is determined by the maximum RAS low time and the CAS page cycle
time used. With minimum CAS page cycle time, all 512 columns specified by column addresses A0 through A8
can be accessed without intervening RAS cycles.
Unlike conventional page mode DRAMs, the column-address buffers in this device are activated on the falling
edge of RAS. The buffers act as transparent or flow-through latches while CAS is high. The column address
latches to the first CAS falling edge. This feature allows the SMJ44C256 to operate at a wider data bandwidth
than conventional page mode parts, since data retrieval begins as soon as column address is valid rather than
when CAS goes low. This performance improvement is referred to as enhanced page mode. Valid column
address can be presented immediately after t_h(RA) (row address hold time) has been satisfied, usually well in
advance of the falling edge of CAS. In this case, data is obtained after t_a(C) maximum (access time from CAS
low), if t_a(CA) maximum (access time from column address) has been satisfied. In the event that column
addresses for the next page cycle are valid at the time CAS goes high, access time for the next cycle is
determined by the later occurrence of t_a(C) or t_a(CP) (access time from rising edge of CAS).
• POST OFFICE BOX 1443 HOUSTON, TEXAS 77251–1443
3