mc68331cpv20b1 Freescale Semiconductor, Inc, mc68331cpv20b1 Datasheet - Page 77

• Manufacturer Part Number: mc68331cpv20b1
• Description: Mc68331 32 Bit Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

4.5.6.1 Slave (Factory Test) Mode Arbitration
4.5.6.2 Show Cycles
MC68331
USER’S MANUAL
State changes occur on the next rising edge of CLKOUT after the internal signal is val-
id. The BG signal transitions on the falling edge of the clock after a state is reached
during which G changes. The bus control signals (controlled by T) are driven by the
MCU immediately following a state change, when bus mastership is returned to the
MCU. State 0, in which G and T are both negated, is the state of the bus arbiter while
the MCU is bus master. Request R and acknowledge A keep the arbiter in state 0 as
long as they are both negated.
This mode is used for factory production testing of internal modules. It is not supported
as a user operating mode. Slave mode is enabled by holding DATA11 low during re-
set. In slave mode, when BG is asserted, the MCU is slaved to an external master that
has full access to all internal registers.
The MCU normally performs internal data transfers without affecting the external bus,
but it is possible to show these transfers during debugging. AS is not asserted exter-
nally during show cycles.
RE-ARBITRATE OR RESUME PROCESSOR
1) ASSERT BUS GRANT (BG)
1) NEGATE BG (AND WAIT FOR
Figure 4-14 Bus Arbitration Flowchart for Single Request
BGACK TO BE NEGATED)
GRANT BUS ARBITRATION
TERMINATE ARBITRATION
OPERATION
MCU
Freescale Semiconductor, Inc.
For More Information On This Product,
SYSTEM INTEGRATION MODULE
Go to: www.freescale.com
1) EXTERNAL ARBITRATION DETERMINES
2) NEXT BUS MASTER WAITS FOR BGACK
3) NEXT BUS MASTER ASSERTS BGACK
4) BUS MASTER NEGATES BR
1) PERFORM DATA TRANSFERS (READ AND
1) NEGATE BGACK
1) ASSERT BUS REQUEST (BR)
NEXT BUS MASTER
TO BE NEGATED
TO BECOME NEW MASTER
WRITE CYCLES) ACCORDING TO THE
SAME RULES THE PROCESSOR USES
ACKNOWLEDGE BUS MASTERSHIP
RELEASE BUS MASTERSHIP
OPERATE AS BUS MASTER
REQUESTING DEVICE
REQUEST THE BUS
BUS ARB FLOW
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