
Advanced Notebook I/O for ISA or LPC Designs
Datasheet
Rev. 0.5 (03-24-05)
Page 44
SMSC SIO10N268
DATASHEET
clocks 1 and 2 of the SYNC phase and ‘0000b’ for the last clock of the SYNC phase. This would be
equivalent to 5 clocks worth of access time if the device started that access at the conclusion of the
MADDR phase. Once SYNC is achieved, the device returns the data in two clocks and gives ownership of
the bus back to the host with a TAR phase.
8.4.7
Write Cycles
8.4.7.1
Single Byte
All devices that support FWH Memory Write cycles must support single byte writes. FWH Memory Write
cycles use the same preamble as FWH Memory read cycles.
To indicate that a single byte transfer cycle is being performed, the master asserts an MSIZE value of 0.
After the address and size has been transferred, the 2-clock data phase begins. Following the data phase,
bus ownership is transferred to the FWH component with a TAR cycle. Following the TAR phase, the
device must assert a SYNC value of ‘0000b’ (ready) or ‘1010b’ (error) indicating the data has been
received. Bus ownership is then given back to the master with another TAR phase.
FWH Memory Writes only allow one clock for the SYNC phase. The TAR+SYNC+TAR phases at the end
of FWH memory write cycles must be exactly 5 clocks.
Preamble
D L
SYNC
CLK
FRAME#
TAR
AD[3:0]
10 Clocks
D H
TAR
Figure 8.3 - Single Byte Write
8.4.8
Error Reporting
There is no error reporting over the FWH interface for FWH Memory cycles. If an error occurs, such as an
address out of range or an unsupported memory size, the cycle will continue from the host unabated. This
is because these errors are the result of illegal programming, and there is no efficient error reporting
method that can be done to counter the programming error.
Therefore, the FWH component must not report the error conditions over the FWH interface. It must only
report wait states and the ‘ready’ condition. It may choose to log the error internally to be debugged, but it
must not signal an error through the FWH interface itself.
8.4.9
FWH Cycle Examples
8.4.9.1
EXAMPLE 1: FWH 1-Byte Read
FIELD
DRIVEN BY
CLOCKS
LAD[3:0]
COMMENT
START
Host
1
1101
LAD[3:0]=1101 (FWH Memory Read)
IDSEL
Host
1
xxxx
LAD[3:0]=selected FWH component
MADDR
Host
1
xxxx
Most significant nibble