TMS416400A, TMS417400A

4194304 BY 4-BIT

DYNAMIC RANDOM-ACCESS MEMORIES

SMKS889B – AUGUST 1996 – REVISED OCTOBER 1997

5

POST OFFICE BOX 1443

operation

enhanced page mode

Enhanced 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

Unlike conventional page-mode DRAMs, the column-address buffers in these devices are activated on the

falling edge of RAS. The buffers act as transparent or flow-through latches while CAS is high. The falling edge

of CAS latches the column addresses and enables the output. This feature allows the devices to operate at a

higher data bandwidth than conventional page-mode devices because data retrieval begins as soon as the

column address is valid rather than when CAS transitions low. This performance improvement is referred to as

enhanced-page mode. A valid column address can be presented immediately after row-address hold time has

event that column address for the next cycle is valid at the time CAS goes high, access time for the next cycle

address: A0 – A11 ( TMS416400A) and A0 – A10 (TMS417400A)

Twenty-two address bits are required to decode each of the 4 194 304 storage cell locations. For the

TMS416400A, 12 row-address bits are set up on A0 through A11 and latched onto the chip by the row-address

strobe (RAS). Ten column-address bits are set up on A0 through A9. For TMS417400A, 11 row-address bits

are set up on inputs A0 through A10 and latched onto the chip by RAS. Eleven column-address bits are set up

on A0 through A10. All addresses must be stable on or before the falling edge of RAS and CAS. RAS is similar

to a chip enable because it activates the sense amplifiers as well as the row decoder. CAS is used as a chip

select, activating the output buffers and latching the address bits into the column-address buffers.

write enable ( W )

The read- or write mode is selected through W. A logic high on W selects the read mode, and a logic low selects

the write mode. The data inputs are disabled when the read mode is selected. When W goes low prior to CAS

(early write), data out remains in the high-impedance state for the entire cycle, permitting a write operation with

OE grounded.

data in (DQ1 – DQ4)

Data is written during a write- or read-modify-write cycle. Depending on the mode of operation, the falling edge

of CAS or W strobes data into the on-chip data latch. In an early-write cycle, W is brought low prior to CAS, and

the data is strobed in by CAS with setup-and-hold times referenced to this signal. In a delayed-write- or

read-modify-write cycle, CAS is already low, and the data is strobed in by W with the setup-and-hold time

referenced to this signal. Also, OE must be high to bring the output buffers to the high-impedance state prior

to impressing data on the I/O lines.

data out (DQ1 – DQ4)

Data out is the same polarity as data in. The output is in the high-impedance (floating) state until CAS and OE