XC2200 Derivatives
System Units (Vol. 1 of 2)
The External Bus Controller EBC
User’s Manual
9-33
V2.1, 2008-08
EBC_X8, V1.0d1
9.4
LXBus Access Control and Signal Generation
Access control to the LXBus
1)
is required for the on-chip peripherals MultiCAN and USIC.
For these accesses, CS7 and its fixed control registers ADDRSEL7, TCONCS7, and
FCONCS7 are used. The address range (from 20’0000
H
to 20’7FFF
H
), defined by the
ADDRSEL7 value of 2003
H
, is located in the ’External IO Area’. Only for the External IO
Area (within the total external address range) it is guaranteed that a read access is
executed after a preceding write access.
The value of the bus function control register FCONCS7 is selected according to the
requirements of the MultiCAN and USIC: 16-bit demultiplexed bus, access time
controlled with synchronous READY. This function control is represented by the
FCONCS7 value of 0027
H
.
The minimum LXBus cycle timing (as controlled with register TCONCS7) will be
lengthened with waitstate(s) controlled by the MultiCAN/USIC itself with the READY
function. This timing control is defined by the TCONCS7 value of 0000
H
.
Accesses to the LXBus do not generate valid external bus cycles on an enabled external
bus interface:
•
the configured chip select signals are driven high
•
the external control signal pins (RD, WR, ALE) are driven inactive and then switched
to input
•
the other bus pins are switched to input, the address lines may reflect the LXBus
address for a short period
Note: In this case, the pins are controlled by their respective IOCR registers (lower 3
bits). It is recommended to activate a pull-up or pull-down device by pre-
configuring the IOCR registers. The default setting leaves the pins floating. In
particular it is strongly recommended to configure pull-ups at least for the control
lines RD and WR, and a pull-down for ALE. External pull resistors serve the same
purpose, of course.
1) The LXBus is an internal (local) extension of the external bus. It is controlled by the EBC identically to the
external bus, using the select and cycle control functions as described for the external bus.