82375EB Datasheet, PDF (111/131 Pages) Intel Corporation – PCI-EISA BRIDGE (PCEB)

82375EB SB
290477 – 74
Figure 30 Copy Function PCI 16-bit Read from a 16-bit EISA or ISA Slave BE 3 0 ^e0011
8 3 The Re-Drive Operation
The re-drive operation (Figure 31) is used when both the master and the slave other than PCEB are on the
EISA Bus and the master slave size combination is mis-matched Specifically re-drive occurs
 during EISA master and DMA cycles (excluding DMA compatible cycles) where the master’s data size is
greater than the slave’s data size
 during EISA master cycles to ISA slaves where the master slave match in the size
 during DMA burst write cycles to a non-burst memory slave
During a re-drive cycle the data is latched from the EISA Bus and then driven back onto the appropriate EISA
byte lanes During a read cycle the re-drive occurs after the necessary sub-cycles have been completed and
the read data has been assembled For example when a 32 bit EISA master (other than PCEB) performs 32
bit read from an 8 bit EISA slave the following sequence of events occurs
1 The 32-bit EISA master initiates the read cycle Since the master slave combination is a mis-match the
master backs off the bus The EISA master floats its START BE 3 0 and SD 31 0 lines The cycle
control is then transferred to the ESC
2 The ESC brings in the first 8 bit data (byte 0) in the first cycle The ESC asserts SDLE0 to the PCEB
3 When SDLE0 is asserted the PCEB latches byte 0 into the least significant byte lane
4 In the second cycle the ESC reads the next 8 bit data (byte 1) The PCEB uses SDLE1 SDCPYUP and
SDCPYEN0-1 to latch byte 1 and copy it to the second least significant byte lane (copy-up) This process
continues for byte 2 and byte 3 On the fourth cycle the Dword assembly is complete During each of the 4
cycles the ESC generates BE 3 0 combinations
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