mc9s12e256 Freescale Semiconductor, Inc, mc9s12e256 Datasheet - Page 533
mc9s12e256
Manufacturer Part Number
mc9s12e256
Description
Hcs12 Microcontrollers 16-bit Microcontroller
Manufacturer
Freescale Semiconductor, Inc
Datasheet
1.MC9S12E256.pdf
(602 pages)
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Company:
Part Number:
mc9s12e256CFUE
Manufacturer:
Freescale Semiconductor
Quantity:
10 000
Company:
Part Number:
mc9s12e256CPVE
Manufacturer:
Freescale Semiconductor
Quantity:
135
Company:
Part Number:
mc9s12e256CPVE
Manufacturer:
FREESCA
Quantity:
300
Company:
Part Number:
mc9s12e256CPVE
Manufacturer:
Freescale Semiconductor
Quantity:
10 000
Company:
Part Number:
mc9s12e256MFUE
Manufacturer:
FREESCAL
Quantity:
329
Company:
Part Number:
mc9s12e256MFUE
Manufacturer:
Freescale Semiconductor
Quantity:
10 000
Company:
Part Number:
mc9s12e256MPVE
Manufacturer:
Freescale Semiconductor
Quantity:
10 000
Company:
Part Number:
mc9s12e256VFUE
Manufacturer:
Freescale Semiconductor
Quantity:
10 000
- Current page: 533 of 602
- Download datasheet (4Mb)
18.4
18.4.1
The external signals LSTRB, R/W, and AB0 indicate the type of bus access that is taking place. Accesses
to the internal RAM module are the only type of access that would produce LSTRB = AB0 = 1, because
the internal RAM is specifically designed to allow misaligned 16-bit accesses in a single cycle. In these
cases the data for the address that was accessed is on the low half of the data bus and the data for
address + 1 is on the high half of the data bus. This is summarized in
18.4.2
In order to allow fast internal bus cycles to coexist in a system with slower external memory resources, the
HCS12 supports the concept of stretched bus cycles (module timing reference clocks for timers and baud
rate generators are not affected by this stretching). Control bits in the MISC register in the MMC sub-block
of the core specify the amount of stretch (0, 1, 2, or 3 periods of the internal bus-rate clock). While
stretching, the CPU state machines are all held in their current state. At this point in the CPU bus cycle,
write data would already be driven onto the data bus so the length of time write data is valid is extended
in the case of a stretched bus cycle. Read data would not be captured by the system until the E clock falling
edge. In the case of a stretched bus cycle, read data is not required until the specified setup time before the
falling edge of the stretched E clock. The chip selects, and R/W signals remain valid during the period of
stretching (throughout the stretched E high time).
Freescale Semiconductor
Functional Description
Detecting Access Type from External Signals
Stretched Bus Cycles
The address portion of the bus cycle is not stretched
LSTRB
1
0
1
0
0
1
0
1
Table 18-15. Access Type vs. Bus Control Pins
AB0
0
1
0
1
0
1
0
1
MC9S12E256 Data Sheet, Rev. 1.08
R/W
1
1
0
0
1
1
0
0
NOTE
8-bit read of an even address
8-bit read of an odd address
8-bit write of an even address
8-bit write of an odd address
16-bit read of an even address
16-bit read of an odd address
(low/high data swapped)
16-bit write to an even address
16-bit write to an odd address
(low/high data swapped)
Chapter 18 Multiplexed External Bus Interface (MEBIV3)
Type of Access
.
Table
18-15.
533
Related parts for mc9s12e256
Image
Part Number
Description
Manufacturer
Datasheet
Request
R
Part Number:
Description:
Manufacturer:
Freescale Semiconductor, Inc
Datasheet:
Part Number:
Description:
Manufacturer:
Freescale Semiconductor, Inc
Datasheet:
Part Number:
Description:
Manufacturer:
Freescale Semiconductor, Inc
Datasheet:
Part Number:
Description:
Manufacturer:
Freescale Semiconductor, Inc
Datasheet:
Part Number:
Description:
Manufacturer:
Freescale Semiconductor, Inc
Datasheet:
Part Number:
Description:
Manufacturer:
Freescale Semiconductor, Inc
Datasheet:
Part Number:
Description:
Manufacturer:
Freescale Semiconductor, Inc
Datasheet:
Part Number:
Description:
Manufacturer:
Freescale Semiconductor, Inc
Datasheet:
Part Number:
Description:
Manufacturer:
Freescale Semiconductor, Inc
Datasheet:
Part Number:
Description:
Manufacturer:
Freescale Semiconductor, Inc
Datasheet:
Part Number:
Description:
Manufacturer:
Freescale Semiconductor, Inc
Datasheet:
Part Number:
Description:
Manufacturer:
Freescale Semiconductor, Inc
Datasheet:
Part Number:
Description:
Manufacturer:
Freescale Semiconductor, Inc
Datasheet:
Part Number:
Description:
Manufacturer:
Freescale Semiconductor, Inc
Datasheet:
Part Number:
Description:
Manufacturer:
Freescale Semiconductor, Inc
Datasheet: