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5962-9161709Q9X 参数 Datasheet PDF下载

5962-9161709Q9X图片预览
型号: 5962-9161709Q9X
PDF下载: 下载PDF文件 查看货源
内容描述: [Dual-Port SRAM, 8KX16, 30ns, CMOS, DIE]
分类和应用: 存储内存集成电路静态存储器异步传输模式ATM
文件页数/大小: 27 页 / 528 K
品牌: ATMEL [ ATMEL ]
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The write pulse to the SLAVE must be inhibited by the MASTER’s maximum arbitration  
time. If a conflict then occurs, the write to the SLAVE will be inhibited because of the  
MASTER’s BUSY signal.  
Semaphore Logic  
The M67025E is an extremely fast dual-port 4 Kb × 16 CMOS static RAM with an additional  
locations dedicated to binary semaphore flags. These flags allow either of the processors on the  
left or right side of the dual-port RAM to claim priority over the other for functions defined by the  
system software. For example, the semaphore flag can be used by one processor to inhibit the  
other from accessing a portion of the dual-port RAM or any other shared resource.  
The dual-port RAM has a fast access time, and the two ports are completely indepen-  
dent of each another. This means that the activity on the left port cannot slow the access  
time of the right port. The ports are identical in function to standard CMOS static RAMs  
and can be read from, or written to, at the same time with the only possible conflict aris-  
ing from simultaneous writing to, or a simultaneous READ/WRITE operation on, a non-  
semaphore location. Semaphores are protected against such ambiguous situations and  
may be used by the system program to prevent conflicts in the non-semaphore segment  
of the dual-port RAM. The devices have an automatic power-down feature controlled by  
CS, the dual-port RAM select and SEM, the semaphore enable. The CS and SEM pins control  
on-chip-power-down circuitry that permits the port concerned to go into stand-by mode when  
not selected. This conditions is shown in Table 1 where CS and SEM are both high.  
Systems best able to exploit the M67025E are based around multiple processors or con-  
trollers and are typically very high-speed, software controlled or software-intensive  
systems. These systems can benefit from the performance enhancement offered by the  
M67025 hardware semaphores, which provide a lock-out mechanism without the need  
for complex programming.  
Software handshaking between processors offers the maximum level of system flexibil-  
ity by permitting shared resources to be allocated in varying configurations. The  
M67025E does not use its semaphore flags to control any resources through hardware,  
thus allowing the system designer total flexibility in system architecture.  
An advantage of using semaphores rather than the more usual methods of hardware  
arbitration is that neither processor ever incurs wait states. This can prove to be a con-  
siderable advantage in very high speed systems.  
How The Semaphore  
Flags Work  
The semaphore logic is a set of eight latches independent of the dual-port RAM. These  
latches can be used to pass a flag or token, from one port to the other to indicate that a  
shared resource is in use. The semaphore provides the hardware context for the “Token  
Passing Allocation’ method of use assignment. This method uses the state of a sema-  
phore latch as a token indicating that a shared resource is in use. If the left processor  
needs to use a resource, it requests the token by setting the latch. The processor then  
verifies that the latch has been set by reading it. If the latch has been set the processor  
assumes control over the shared resource. If the latch has not been set, the left proces-  
sor has established that the right processor had set the latch first, has the token and is  
using the shared resource. The left processor may then either repeatedly query the sta-  
tus of the semaphore, or abandon its request for the token and perform another  
operation whilst occasionally attempting to gain control of the token through a set and  
test operation. Once the right side has relinquished the token the left side will be able to  
take control of the shared resource.  
The semaphore flags are active low. A token is requested by writing a zero to a sema-  
phore latch, and is relinquished again when the same side writes a one to the latch.  
5
M67025E  
4146J–AERO–06/03  
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