82375EB Datasheet, PDF (110/131 Pages) Intel Corporation – PCI-EISA BRIDGE (PCEB)

82375EB SB
290477 – 73
Figure 29 Assembly Function PCI 32-bit Read from an 8-bit EISA or ISA SlaveBE 3 0 ^e0000
8 2 The Copy Operation (Up Or Down)
The copy operation (Figure 30) is invoked during data transfers between byte lanes This operation allows the
assembly disassembly of the data pieces during the cycles between mismatched master slave combinations
For example Section 8 1 Data Assembly and Disassembly describes a 32-bit master read from an 8-bit slave
where the data is copied up during the assembly process Copy-up is used for data assembly and copy-down
is used for data disassembly
The copy-up and copy-down operations are also used during transfers where assembly or disassembly are not
required These transfers are
 When the master size is smaller than the slave size (e g 16-bit EISA master cycle to a 32-bit EISA slave)
 Between a mis-matched master slave combination when only a byte or a word needs to be transferred
(e g 32-bit EISA master cycle to an 8-bit ISA slave and only a byte needs to be transferred)
The number of bytes copied up or down is a function of the number of bytes requested (BE 3 0 ) and the
master slave size combinations During EISA master cycles where the data copying is performed cycle
control is transferred from the bus master to the ESC except during transfers where the master’s data size is
smaller than the slave’s data size During DMA transfers bus control is maintained by the ESC throughout the
transfer
110