Freescale Semiconductor MPC8260 8.4.3.6 Effect of Port Size on Data Transfers

The 60x Bus
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
8-16 Freescale Semiconductor
8.4.3.6 Effect of Port Size on Data Transfers
The PowerQUICC II can transfer operands through its 64-bit data port. If the transfer is controlled by the
internal memory controller, the PowerQUICCII can support 8-, 16-, 32-, and 64-bit data port sizes as
demonstrated in Figure 8-6. The bus requires that the portion of the data bus used for a transfer to or from
a particular port size be fixed. A 64-bit port must reside on data bus bits D[0–63], a 32-bit port must reside
on bits D[0–31], a 16-bit port must reside on bits D[0–15], and an 8-bit port must reside on bits D[0–7].
The PowerQUICC II always tries to transfer the maximum amount of data on all bus cycles: for a word
operation, it always assumes the port is 64 bits wide when beginning the bus cycle; for burst and extended
byte cycles, a 64-bit bus is assumed.
Figure 8-6. shows the device connections on the data bus. Tabl e 8-8 lists the bytes required on the data bus
for read cycles.
Misaligned—1st access 010 110 —————— A A
2nd access 0 1 0 0 0 0 A A ——————
Misaligned—1st access 001 111 ——————— A
2nd access 0 1 1 0 0 0 A A A —————
1A: Byte lane used
2—: Byte lane not used
Table8-7. Unaligned Data Transfer Example (4-Byte Example) (continued)
Program Size of
Word (4 bytes) TSIZ[1–3] A[29–31]
Data Bus Byte Lanes
D0... ...D31 D32... ...D63
B0 B1 B2 B3 B4 B5 B6 B7