Information

Enhanced Local Bus Controller
MPC8308 PowerQUICC II Pro Processor Reference Manual, Rev. 1
Freescale Semiconductor 10-85
10.5.2 Interface to Different Port-Size Devices
The eLBC supports 8- and 16-bit data port sizes. However, the bus requires that the portion of the data bus
used for a transfer to or from a particular port size be fixed. A 16-bit port must reside on LD[0:15], and an
8-bit port must reside on LD[0:7]. The local bus always tries to transfer the maximum amount of data on
all bus cycles. Figure 10-71 shows the device connections on the data bus.
Figure 10-71. Interface to Different Port-Size Devices
Table 10-43 lists the bytes required on the data bus for read cycles.
Table 10-43. Data Bus Drive Requirements For Read Cycles
Transfer
Size
Address
State
1
3 lsbs
Port Size/LD Data Bus Assignments
16-Bit 8-Bit
0–7 8–15 16–23 24–31 0–7 8–15 16–23 24–31
Byte 000 OP0 —
OP0
001 — OP1 OP1
010 OP2 — OP2
011 — OP3 OP3
100 OP4 — OP4
101 — OP5 OP5
110 OP6 — OP6
111 — OP7 OP7
0
31 63
OP0 OP1 OP2 OP3 OP4 OP5 OP6 OP7
LD[0:7] LD[8:15]
OP0 OP1
OP2 OP3
OP4 OP5
OP6 OP7
OP0
OP7
Interface Output Register
16-Bit Port Size
8-Bit Port Size