MSM5718B70 View Datasheet(PDF) - Oki Electric Industry
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MFG CO.
'MSM5718B70' PDF : 40 Pages View PDF
MSM5718B70
¡ Semiconductor
RANDOM ACCESS MODE
Non-contiguous blocks of memory can be accessed through the use of the read and write non-
sequential (Random Access) operations. With these commands multiple eight-byte blocks (octbytes)
of data within an open page can be accessed in any order. To do this, the master device sends a request
packet specifying a non-sequential operation along with the address of the first octbyte to be
accessed. The master device also generates a serial address packet (see Fig. 9) on the BusEnable signal
that specifies the address of the next octbyte. Successive serial address packets continue to specify
new addresses within the open page while data is continuously transferred until the access is
complete.
Random access mode can be used to satisfy the burst order of processors like the Intel™ Pentium™
at full RDRAM bandwidth.
BIT MASKING
Three forms of bit masking are available for memory write operations. These operations are referred
to as data-per-bit (Dpb), mask-per-bit (Mpb), and both-per-bit (Bpb) masking. An eight-byte Mask
Data register (MDReg) within the RDRAM is used to hold the static value of either mask or data
information for these operations. The Mask Data register is an RDRAM internal register that is
written by the Bpb commands, and is used by the Mpb and Dpb commands.
With the Dpb operation, the MDReg is used to hold a static mask that is applied to all octbytes of data
written to the RDRAM core. With the Mpb operation, the MDReg is used to hold an octbyte of static
data that is masked by dynamic bit masks supplied in the data packets before being written to the
RDRAM core.
The Bpb operation requires data packets to alternate between mask and data octbytes. The even data
packets (starting with data packet 0) carry bit masking information which is placed in the MDReg
while the odd data packets carry the data to be masked by the latest contents on the MDReg. This
type of operation is also used to set the MDReg for later use in Dpb and Mpb operations.
Table 6 shows the source of the mask and data for each of the write commands. The first eight
columns show the Wseq and Wnsq sequential and non-sequential (fandom-access) write commands.
Each has four bit mask sub-commands: Npb, Dpb, Mpb, and Bpb.
A write command consists of writing from one to 32 octbytes of data W[31:0]. Each octbyte of data
is masked by an octbyte of bitmask Bit[31:0]; that is, if the bitmask bit is set, then the corresponding
bit of write data is written. If the bitmask bit is clear, then the bit in memory is left unchanged.
Each of the first eight columns of Table 6 shows the source of the up-to-32 octbytes of write data and
bitmask for the eight write commands. The Npb commands use no bitmask at all - effectively the
bitmask is all ones. The Dpb command takes a single octbyte of bitmask from the MDReg and applies
it to all data octbytes that are written. The Dpb command does the reverse and takes a single octbyte
of write data from the MDReg and writes it to each octbyte of memory using a different bitmask from
the data packet. The Bpb commands take an octbyte of bitmask and an octbyte of write data
alternately, and writes them to a single octbyte of memory.
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