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参数资料
| 型号： | DS1609 |
| 厂商： | DALLAS SEMICONDUCTOR |
| 元件分类： | DRAM |
| 英文描述： | Dual Port RAM(双端口RAM) |
| 中文描述： | 256 X 8 DUAL-PORT SRAM, 50 ns, PDIP24 |
| 封装： | 0.600 INCH, PLASTIC, DIP-24 |
| 文件页数： | 2/7页 |
| 文件大小： | 56K |
| 代理商： | DS1609 |
DS1609
021998 2/7
ance operation at reduced voltage can be achieved
down to 2.5 volts.
OPERATION – READ CYCLE
The main elements of the dual port RAM are shown in
Figure 1.
A read cycle to either port begins by placing an address
on the multiplexed bus pins AD0 - AD7. The port enable
control (CE) is then transitioned low. This control signal
causes address to be latched internally. Addresses can
be removed from the bus provided address hold time is
met. Next, the output enable control (OE) is transitioned
low, which begins the data access portion of the read
cycle. With both CE and OE active low, data will appear
valid after the output enable access time t
OEA
. Data will
remain valid as long as both port enable and output en-
able remains low. A read cycle is terminated with the
first occurring rising edge of either CE or OE. The ad-
dress/data bus will return to a high impedance state af-
ter time t
CEZ
or t
OEZ
as referenced to the first occurring
rising edge. WE must remain high during read cycles.
OPERATION – WRITE CYCLE
A write cycle to either port begins by placing an address
on the multiplexed bus pins AD0 - AD7. The port enable
control (CE) is then transitioned low. This control signal
causes address to be latched internally. As with a read
cycle, the address can be removed from the bus pro-
vided address hold time is met. Next the write enable
control signal (WE) is transitioned low which begins the
write data portion of the write cycle. With both CE and
WE active low the data to be written to the selected
memory location is placed on the multiplexed bus. Pro-
vided that data setup (t
DS
) and data hold (t
DH
) times are
met, data is written into the memory and the write cycle
is terminated on the first occurring rising edge of either
CE or WE. Data can be removed from the bus as soon
as the write cycle is terminated. OE must remain high
during write cycles.
ARBITRATION
The DS1609 dual port RAM has a special cell design
that allows for simultaneous accesses from two ports
(see Figure 2). Because of this cell design, no arbitra-
tion is required for read cycles occurring at the same in-
stant. However, an argument for arbitration can be
made for reading and writing the cell at the exact same
instant or for writing from both ports at the same instant.
If a write cycle occurs while a read cycle is in progress,
the read cycle will likely recover either the old data or
new data and not some combination of both. However,
the write cycle will update the memory with correct data.
Simultaneous write cycles to the same memory location
pose the additional concern that the cell may be in con-
tention causing a metastable state. Depending on the
timing of the write cycles of port A and port B, the
memory location could be left containing the data writ-
ten from port A or the data from port B or some combina-
tion thereof. However, both concerns expressed above
can be eliminated by disciplined system software de-
sign. A simple way to assure that read/write conflicts
don’t occur is to perform redundant read cycles. Write/
write arbitration needs can be avoided by assigning
groups of addresses for write operation to one port only.
Groups of data can be assigned check sum bytes which
would guarantee correct transmission. A software arbi-
tration system using a “mail box” to pass status informa-
tion can also be employed. Each port could be assigned
a unique byte for writing status information which the
other port would read. The status information could tell
the reading port if any activity is in progress and indicate
when activity is going to occur.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| DS1609-35 | 制造商:未知厂家 制造商全称:未知厂家 功能描述:x8 Dual-Port SRAM |
| DS1609-50 | 功能描述:RAM其它 RoHS:否 制造商:Freescale Semiconductor 封装:Tray |
| DS1609-50+ | 功能描述:RAM其它 Dual Port RAM RoHS:否 制造商:Freescale Semiconductor 封装:Tray |
| DS1609N-35 | 制造商:未知厂家 制造商全称:未知厂家 功能描述:x8 Dual-Port SRAM |
| DS1609N-50 | 制造商:未知厂家 制造商全称:未知厂家 功能描述:x8 Dual-Port SRAM |
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