MC68HC16Z1CAG16 Datasheet, PDF (153/500 Pages) Freescale Semiconductor, Inc – M68HC16Z Series users manual

Freescale Semiconductor, Inc.
MCU
GRANT BUS ARBITRATION
1) ASSERT BUS GRANT (BG)
TERMINATE ARBITRATION
1) NEGATE BG (AND WAIT FOR
BGACK TO BE NEGATED)
RE-ARBITRATE OR RESUME PROCESSOR
OPERATION
REQUESTING DEVICE
REQUEST THE BUS
1) ASSERT BUS REQUEST (BR)
ACKNOWLEDGE BUS MASTERSHIP
1) EXTERNAL ARBITRATION DETERMINES
NEXT BUS MASTER
2) NEXT BUS MASTER WAITS FOR BGACK
TO BE NEGATED
3) NEXT BUS MASTER ASSERTS BGACK
TO BECOME NEW MASTER
4) BUS MASTER NEGATES BR
OPERATE AS BUS MASTER
1) PERFORM DATA TRANSFERS (READ AND
WRITE CYCLES) ACCORDING TO THE SAME
RULES THE PROCESSOR USES
RELEASE BUS MASTERSHIP
1) NEGATE BGACK
Figure 5-17 Bus Arbitration Flowchart for Single Request
BUS ARB FLOW
5.6.6.1 Show Cycles
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.
Show cycles are controlled by the SHEN[1:0] in SIMCR. This field is set to %00 by re-
set. When show cycles are disabled, the address bus, function codes, size, and read/
write signals reflect internal bus activity, but AS and DS are not asserted externally and
external data bus pins are in high-impedance state during internal accesses. Refer to
5.2.3 Show Internal Cycles and the SIM Reference Manual (SIMRM/AD) for more
information.
When show cycles are enabled, DS is asserted externally during internal cycles, and
internal data is driven out on the external data bus. Because internal cycles normally
continue to run when the external bus is granted, one SHEN[1:0] encoding halts inter-
nal bus activity while there is an external master.
SIZ[1:0] signals reflect bus allocation during show cycles. Only the appropriate portion
of the data bus is valid during the cycle. During a byte write to an internal address, the
portion of the bus that represents the byte that is not written reflects internal bus con-
ditions, and is indeterminate. During a byte write to an external address, the data mul-
tiplexer in the SIM causes the value of the byte that is written to be driven out on both
bytes of the data bus.
M68HC16 Z SERIES
USER’S MANUAL
SYSTEM INTEGRATION MODULE
For More Information On This Product,
Go to: www.freescale.com
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