External Bus Interface (EBI)
MPC5510 Microcontroller Family Reference Manual, Rev. 1
Freescale Semiconductor
29-7
Preliminary
29.2.1.12 WE[0:3] — Write Enables 0-3
Write enables are used to enable program operations to a particular memory WE[0:3] are only asserted for
chip-select accesses.
For chip-select accesses to a 16-bit port, only WE[0:1] are used by the EBI, regardless of which half of the
DATA bus is selected via the D16_31 bit in the EBI_MCR.
29.2.2
Signal Function and Direction by Mode
The EBI operating mode is configured using two fields in the EBI master control register (EBI_MCR):
EXTM and MDIS. Their settings determine which EBI signals are valid and the I/O direction. When a
signal is configured for non-EBI function in the EBI_MCR, the EBI always negates the signal if the EBI
controls the corresponding pad (determined by SIU configuration).
lists the function and
direction of the external signals in each of the EBI modes of operation. The clock signals are not included
because they are output only (from the FMPLL module) and are not affected by EBI modes. See
Section 29.3.2.3, “EBI Module Configuration Register (EBI_MCR)
,” for details on the EXTM and MDIS
bits.
Table 29-1. Signal Function (
f
) According to EBI Mode Settings
Signal Name
Modes
Module Disable
f
EXTM = n, MDIS = 1
Single Master
f
I/O Direction
EXTM = 0, MDIS = 0
External Master
f
I/O Direction
EXTM = 1, MDIS = 0
BDIP
non-EBI function
Burst data in progress
(Output)
1
Not supported
CS[0:3]
non-EBI function
Chip selects (Output)
AD[0:31]
non-EBI function
Multiplexed Address and
Data bus (I/O)
ADDR[8:15]
non-EBI function
Non-multiplexed Address
(O)
OE
non-EBI function
Output enable (Output)
RD_WR
non-EBI function
Read_Write (Output)
TA
non-EBI function
Transfer acknowledge
(I/O)
TEA
non-EBI function
Transfer error
acknowledge (I/O)
TS
non-EBI function
Transfer start (Output)
ALE
non-EBI function
Address latch enable
(Output)
WE[0:3]
non-EBI function
Write/Byte enables
