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MU9C2485A-90TCI 参数 Datasheet PDF下载

MU9C2485A-90TCI图片预览
型号: MU9C2485A-90TCI
PDF下载: 下载PDF文件 查看货源
内容描述: WidePort LANCAM㈢家庭 [WidePort LANCAM㈢ Family]
分类和应用: 局域网
文件页数/大小: 28 页 / 161 K
品牌: MUSIC [ MUSIC SEMICONDUCTORS ]
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WidePort LANCAM® Family  
OPERATIONAL CHARACTERISTICS Continued  
To operate the daisy chain, the Device Select registers are  
set to FFFFH to enable all devices to execute Command  
Write and Data Write cycles. In normal operation, read  
cycles are enabled from the device with the highest-priority  
match by locking the daisy chain (see “Locked Daisy Chain”  
section). An individual device in the chain may be targeted  
for a read or write operation by temporarily setting the  
Device Select registers to the page address of the target  
device. Setting the Device Select registers back to FFFFH  
restores the operation of the entire daisy chain.  
/E  
/EC  
/EC (INT)  
/MF  
Match Flag Cascading  
Figure 6: /EC(Int) Timing Diagram  
The Match Flag daisy chain cascading is used for three  
purposes: first, to allow operations on Highest-priority  
Match addresses to be issued globally over the whole  
string; second, to provide a system wide match flag;  
third, to lock out all devices except the one with the  
Highest-Priority match for instructions such as Status  
reads after a match. The Match flag logic causes only  
the highest-priority device to operate on its Highest-priority  
Match location while devices with lower-priority matches  
ignore Highest-priority Match operations. The lock-out feature  
is enabled by the match flag cascading and the use of the /EC  
control signal, as shown in Tables 6a and 6b.  
COMPARE OPERATIONS  
During a Compare operation, the data in the Comparand  
register is compared to all locations in the Memory array  
simultaneously. Any mask register used during compares must  
be selected beforehand in the Control register. There are two  
ways compares are initiated: Automatic and Forced compares.  
Automatic compares perform a compare of the contents of the  
Comparand register against Memory locations that are tagged  
as “Valid,” and occur whenever the following happens:  
Ø The Destination Segment counter in the Segment  
Control register reaches its end limit during writes to  
the Comparand or mask registers.  
Ø After a command write of a TCO CT is executed (except  
for a software reset), so that a compare is executed  
with the new settings of the Control register.  
The ripple delay of the flags when connected in a daisy  
chain may require the extension of the /E HIGH time until  
the logic in all devices has settled out. In a string of “n”  
devices, the /E HIGH time should be greater than:  
tEHMFV + (n-2)· tMIVMFV  
Forced compares are initiated by CMP instructions  
using one of the four validity conditions, V, R, S, and E. The  
forced compare against “Empty” locations automatically  
masks all 64 bits of data to find all locations with the validity  
bits set to “Empty”, while the other forced compares are  
only masked as selected in the Control register.  
If the last device’s Match flag is required by external  
logic or a state machine before the start of the next CAM  
cycle, one additional tMIVMFV should be added to the  
/E HIGH time along any required setup time and delays  
for the external logic.  
VERTICAL CASCADING  
Locked Daisy Chain  
In a locked daisy chain, the highest-priority device is the  
one with /MI HIGH and /MF LOW. In Standard mode, only  
this device will respond to command and data reads and  
writes, until the daisy chain has been unlocked by taking  
/EC HIGH. This allows reading the associated data field  
from only the Highest-Priority Match location anywhere in  
a string of devices, or the Match address from the Status  
register of the device with the match. It also permits  
updating the entry stored at the Highest-Priority Match  
location. In Enhanced mode, devices are enabled to respond  
to some command and data writes, as noted in Tables 6a  
and 6b, but not command and data reads.  
WidePort LANCAMs can be vertically cascaded to  
increase system depth. Through the use of flag daisy-  
chaining, multiple devices will respond as an integrated  
system. The flag daisy chain allows all commands to be  
issued globally, with a response only in the device  
containing the Highest-Priority Matching or Next Free  
location. When connected in a daisy chain, the last device’s  
Full flag and Match flag accurately report the condition for  
the whole string. A system in which WidePort LANCAMs  
are vertically cascaded using daisy-chaining of the flags is  
shown in Figure 1a.  
Rev. 2  
14  
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