External Memory Controller (EMC)
Symphony DSP56724/DSP56725 Multi-Core Audio Processors, Rev. 0
Freescale Semiconductor
21-87
21.5
Application Information
21.5.1
Interfacing to Peripherals
21.5.1.1
Multiplexed Address and Data Bus and Unmultiplexed Address Signals
To save pins on the EMC, the address and data are multiplexed onto the same 24-bit bus. An external latch
is needed to unmultiplex and reconstruct the original address. No external intelligence is needed, because
the LALE signal provides the correct timing to control a standard logic latch. The LAD pins can be directly
connected to the data signals of the memory/peripheral.
Transactions on the EMC start with an address phase, where the EMC drives the transaction address on
the LAD signals and asserts the LALE signal. This can be used to latch the address, and then the EMC can
continue with the data phase.
In addition, the EMC supports burst transfers (not in the GPCM machine). LA[2:0] are the burst addresses
within a natural 8-word burst. To minimize the amount of address phases needed on the EMC and to
optimize the throughput, those signals are driven separately and should be used whenever a device requires
the three least significant addresses. Those should not be used from LAD[2:0]. All other addresses,
A[23:3], must be reconstructed through the latch.
Figure 21-49. Multiplexed Address and Data Bus
Muxed Address and Data
Unmuxed Address
LA[2:0]
LAD[23:0]
LALE
EMC
Latch
A[23:3]
D
Q
LE
A[2:0]
D[23:0]