20-4
MCF5272 User’s Manual
Bus Exception: Double Bus Fault
The MCF5272 edge-detects and retimes the TA input. This means that an additional wait
state may or may not be inserted. For example if the active chip select is used to
immediately generate the TA input, one or two wait states may be inserted in the bus access.
The TA signal function is not available after reset. It must be enabled by configuring the
appropriate pin configuration register bits along with the value of CSORn[WS]. If TA is not
used, it should either have a pullup resistor or be driven through gating logic that always
ensures the input is inactive. TA should be negated on the negating edge of the active chip
select.
TA must always be negated before it can be recognized as asserted again. If held asserted
into the following bus cycle, it has no effect and does not terminate the bus cycle.
NOTE:
For the MCF5272 to accept the transfer as successful with a
transfer acknowledge, TEA must be negated throughout the
transfer.
TA is not used for termination during SDRAM accesses.
20.2.5 Transfer Error Acknowledge (TEA)
An external slave asserts this active-low input signal to abort a transfer. The assertion of
TEA immediately aborts the bus cycle. The assertion of TEA has precedence over the
assertion of TA.
The MCF5272 edge-detects and retimes the TEA input. TEA is an asynchronous input
signal.
The TEA signal function is available after reset. If TEA is not used, a pullup resistor or
gating logic must be used to ensure the input is inactive. TEA should be negated on the
negating edge of the active chip select. TEA must always be negated before it can be
recognized as asserted again. If held asserted into the following bus cycle, it has no effect
and does not abort the bus cycle.
TEA has no affect during SDRAM accesses.
20.3 Bus Exception: Double Bus Fault
When a bus error or an address error occurs during the exception processing sequence for
a previous bus error, a previous address error, or a reset exception, the bus or address error
causes a double bus fault. If the MCF5272 experiences a double bus fault, it enters the
halted state. To exit the halt state, reset the MCF5272.
Содержание DigitalDNA ColdFire MCF5272
Страница 1: ...MCF5272UM D Rev 0 02 2001 MCF5272 ColdFire Integrated Microprocessor User s Manual ...
Страница 38: ...xxxviii MCF5272 User s Manual TABLES Table Number Title Page Number ...
Страница 58: ...1 10 MCF5272 User s Manual MCF5272 Specific Features ...
Страница 90: ...2 42 MCF5272 User s Manual Exception Processing Overview ...
Страница 96: ...3 6 MCF5272 User s Manual MAC Instruction Execution Timings ...
Страница 158: ...5 46 MCF5272 User s Manual Motorola Recommended BDM Pinout ...
Страница 184: ...7 12 MCF5272 User s Manual Interrupt Controller Registers ...
Страница 338: ...13 44 MCF5272 User s Manual Application Examples ...
Страница 414: ...18 6 MCF5272 User s Manual PWM Programming Model ...
Страница 452: ...19 38 MCF5272 User s Manual Power Supply Pins ...
Страница 482: ...20 30 MCF5272 User s Manual Reset Operation ...
Страница 492: ...21 10 MCF5272 User s Manual Non IEEE 1149 1 Operation ...
Страница 548: ...INDEX Index 12 MCF5272 User s Manual ...