Document Number: 002-12878 Rev. *F Page 75 of 146
8.3.16 Set Burst Length (SBL 77h)
The Set Burst Length (SBL) command is used to configure the Burst Wrap feature. Burst Wrap is used in conjunction with Quad I/O
Read and DDR Quad I/O Read, in QIO or QPI modes, to access a fixed length and alignment of data. Certain applications can
benefit from this feature by improving the overall system code execution performance. The Burst Wrap feature allows applications
that use cache, to start filling a cache line with instruction or data from a critical address first, then fill the remainder of the cache line
afterwards within a fixed length (8/16/32/64-bytes) of data, without issuing multiple read commands.
The Set Burst Length command is initiated by driving the CS# pin LOW and then shifting the instruction code “77h” followed by 24
dummy bits and 8 “Wrap Length Bits (WL[7]-WL[0])”. The command sequence is shown in Figure 61 on page 76 and Figure 62 on
page 76. Wrap Length bit WL[7] and the lower nibble WL[3:0] are not used. See Configuration Register 3 (CR3V[6:4]) for the
encoding of WL[6]-WL[4] in Section 6.6.5 Configuration Register 3 on page 34.
Once WL[6:4] is set by a Set Burst Length command, all the following “Quad I/O Read” commands will use the WL[6:4] setting to
access the 8/16/32/64-byte section of data. Note, Configuration Register 1 Quad bit CR1V[1] or Configuration Register 2 QPI bit
CR2V[3] must be set to 1 in order to use the Quad I/O read and Set Burst Length commands. To exit the “Wrap Around” function and
return to normal read operation, another Set Burst with Wrap command should be issued to set WL4 = 1. The default value of
WL[6:4] upon power on, hardware or software reset as set in the CR2NV[6:4]. Use WRR or WRAR command to set the default wrap
length in CR2NV[6;4].
The Set Burst Length (SBL) command writes only to CR3V[6:4] bits to enable or disable the wrapped read feature and set the wrap
boundary. The SBL command cannot be used to set the read latency in CR3V[3:0]. The WRAR command must be used to set the
read latency in CR3V or CR3NV.
See Table 35 on page 75 for CR3V[6:5] values for wrap boundary's and start address. When enabled the wrapped read feature
changes the related read commands from sequentially reading until the command ends, to reading sequentially wrapped within a
group of bytes.
When the wrap mode is not enabled (Table 16 on page 34 and Table 19 on page 37), an unlimited length sequential read is
performed.
When the wrap mode is enabled (Table 16 and Table 19) a fixed length and aligned group of 8-, 16-, 32-, or 64-bytes is read starting
at the byte address provided by the read command and wrapping around at the group alignment boundary.
The group of bytes is of length and aligned on an 8-, 16-, 32-, or 64-byte boundary. CR3V[6:5] selects the boundary. See
Section 6.6.5.2 Configuration Register 3 Volatile (CR3V) on page 37.
The starting address of the read command selects the group of bytes and the first data returned is the addressed byte. Bytes are
then read sequentially until the end of the group boundary is reached. If the read continues the address wraps to the beginning of the
group and continues to read sequentially. This wrapped read sequence continues until the command is ended by CS# returning
HIGH.
Table 35. Example Burst Wrap Sequences
CR3V
Value
(Hex)
Wrap
Boundary
(Bytes)
Start
Address
(Hex)
Address Sequence (Hex)
1X Sequential XXXXXX03 03, 04, 05, 06, 07, 08, 09, 0A, 0B, 0C, 0D, 0E, 0F, 10, 11, 12, 13, 14, 15, 16, 17, 18, ...
00 8 XXXXXX00 00, 01, 02, 03, 04, 05, 06, 07, 00, 01, 02, ...
00 8 XXXXXX07 07, 00, 01, 02, 03, 04, 05, 06, 07, 00, 01, ...
01 16 XXXXXX02 02, 03, 04, 05, 06, 07, 08, 09, 0A, 0B, 0C, 0D, 0E, 0F, 00, 01, 02, 03, ...
01 16 XXXXXX0C 0C, 0D, 0E, 0F, 00, 01, 02, 03, 02, 03, 04, 05, 06, 07, 08, 09, 0A, 0B, 0C, 0D, 0E, ...
02 32 XXXXXX0A 0A, 0B, 0C, 0D, 0E, 0F, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 1A, 1B, 1C, 1D, 1E, 1F, 00,
01, 02, 03, 04, 05, 06, 07, 08, 09, 0A, 0B, 0C, 0D, 0E, 0F, ...
02 32 XXXXXX1E 1E, 1F, 00, 01, 02, 03, 04, 05, 06, 07, 08, 09, 0A, 0B, 0C, 0D, 0E, 0F, 10, 11, 12, 13, 14, 15,
16, 17, 18, 19, 1A, 1B, 1C, 1D, 1E, 1F, 00, ...
03 64 XXXXXX03
03, 04, 05, 06, 07, 08, 09, 0A, 0B, 0C, 0D, 0E, 0F, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 1A,
1B, 1C, 1D, 1E, 1F, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 2A, 2B, 2C, 2D, 2E, 2F, 30, 31,
32, 33, 34, 35, 36, 37, 38, 39, 3A, 3B, 3C, 3D, 3E, 3F, 00, 01, 02, ...
03 64 XXXXXX2E
2E, 2F, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 3A, 3B, 3C, 3D, 3E, 3F, 00, 01, 02, 03, 04, 05,
06, 07, 08, 09, 0A, 0B, 0C, 0D, 0E, 0F, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 1A, 1B, 1C,
1D, 1E, 1F, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 2A, 2B, 2C, 2D,, ...