參數(shù)資料
型號: μPD45128441
廠商: NEC Corp.
英文描述: 128M-bit Synchronous DRAM(128M 同步DRAM)
中文描述: 128兆位同步DRAM(128M的同步DRAM)的
文件頁數(shù): 21/84頁
文件大?。?/td> 693K
代理商: ΜPD45128441
Preliminary Data Sheet
21
μ
PD45128441, 45128841, 45128163
6. Programming the Mode Register
The mode register is programmed by the Mode register set command using address bits A13 through A0 as data
inputs. The register retains data until it is reprogrammed or the device loses power.
The mode register has four fields;
Options
/CAS latency : A6 through A4
Wrap type
: A3
Burst length
: A2 through A0
: A13 through A7
Following mode register programming, no command can be issued before at least 2 CLK have elapsed.
/CAS Latency
/CAS latency is the most critical of the parameters being set. It tells the device how many clocks must elapse
before the data will be available.
The value is determined by the frequency of the clock and the speed grade of the device.
13.3 Relationship
between Frequency and Latency
shows the relationship of /CAS latency to the clock period and the speed grade of
the device.
Burst Length
Burst Length is the number of words that will be output or input in a read or write cycle. After a read burst is
completed, the output bus will become Hi-Z.
The burst length is programmable as 1, 2, 4, 8 or full page.
Wrap Type (Burst Sequence)
The wrap type specifies the order in which the burst data will be addressed. This order is programmable as either
“Sequential” or “Interleave”. The method chosen will depend on the type of CPU in the system.
Some microprocessor cache systems are optimized for sequential addressing and others for interleaved
addressing.
7.1 Burst Length and Sequence
shows the addressing sequence for each burst length using them.
Both sequences support bursts of 1, 2, 4 and 8. Additionally, sequence supports the full page length.
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