Information

Table 29-1. FlexBus signal descriptions (continued)
Signal I/O Function
FB_TSIZ1–FB_TSIZ0 O Transfer Size—Indicates (along with FB_TBST) the data transfer size of the current
bus operation. The interface supports 8-, 16-, and 32-bit operand transfers and allows
accesses to 8-, 16-, and 32-bit data ports.
• 00b = 4 bytes
• 01b = 1 byte
• 10b = 2 bytes
• 11b = 16 bytes (line)
For misaligned transfers, FB_TSIZ1–FB_TSIZ0 indicate the size of each transfer. For
example, if a 32-bit access through a 32-bit port device occurs at a misaligned offset of
1h, 8 bits are transferred first (FB_TSIZ1–FB_TSIZ0 = 01b), 16 bits are transferred
next at offset 2h (FB_TSIZ1–FB_TSIZ0 = 10b), and the final 8 bits are transferred at
offset 4h (FB_TSIZ1–FB_TSIZ0 = 01b).
For aligned transfers larger than the port size, FB_TSIZ1–FB_TSIZ0 behave as follows:
• If bursting is used, FB_TSIZ1–FB_TSIZ0 are driven to the transfer size.
• If bursting is inhibited, FB_TSIZ1–FB_TSIZ0 first show the entire transfer size
and then show the port size.
For burst-inhibited transfers, FB_TSIZ1–FB_TSIZ0 change with each
FB_TS assertion
to reflect the next transfer size.
For transfers to port sizes smaller than the transfer size, FB_TSIZ1–FB_TSIZ0 indicate
the size of the entire transfer on the first access and the size of the current port transfer
on subsequent transfers. For example, for a 32-bit write to an 8-bit port, FB_TSIZ1–
FB_TSIZ0 are 00b for the first transaction and 01b for the next three transactions. If
bursting is used for a 32-bit write to an 8-bit port, FB_TSIZ1–FB_TSIZ0 are driven to
00b for the entire transfer.
FB_TBST O Transfer Burst—Indicates that a burst transfer is in progress as driven by the chip. A
burst transfer can be 2 to 16 beats depending on FB_TSIZ1–FB_TSIZ0 and the port
size.
Note: When a burst transfer is in progress (FB_TBST = 0b), the transfer size is 16
bytes (FB_TSIZ1–FB_TSIZ0 = 11b), and the address is misaligned within the
16-byte boundary, the external memory or peripheral must be able to wrap
around the address.
Table continues on the next page...
Signal descriptions
K20 Sub-Family Reference Manual, Rev. 1.1, Dec 2012
646
Preliminary
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