tmp19a61f10xbg TOSHIBA Semiconductor CORPORATION, tmp19a61f10xbg Datasheet - Page 218

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tmp19a61f10xbg

Manufacturer Part Number
tmp19a61f10xbg
Description
32-bit Tx System Risc Tx19 Family
Manufacturer
TOSHIBA Semiconductor CORPORATION
Datasheet

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8.5 Bus Arbitration
The TMP19A61 can be connected to an external bus master. The arbitration of bus control
authority with the external bus master is executed by using the two signals, BUSRQ and
buses only, and cannot acquire control authority for internal buses.
(1) Accessible range of external bus master
(2) Acquisition of bus control authority
BUSAK . The external bus master can acquire control authority for TMP19A61 external
and cannot acquire control authority for internal buses (G-BUS). Therefore, the external
bus master cannot access the internal memories or the internal I/O. The arbitration of
bus control authority for external buses is executed by the external bus interface circuit
(EBIF), and this is independent of the CPU and the internal DMAC. Even when the
external bus master holds the external bus control authority, the CPU and the internal
DMAC can access the internal ROM, RAM and registers. On the other hand, if the CPU
or the internal DMAC tries to access an external memory when the external bus master
holds the external bus control authority, the CPU or the internal DMAC bus cycle has to
wait until the external bus master releases the bus. For this reason, if the BUSRQ
remains active, the TMP19A61 may lock.
bus cycles on the internal buses (G-BUS) and determines whether or not to give the bus
control authority to the external bus master. When it gives the bus control authority to the
external bus master, it asserts the BUSAK signal. At the same time, it makes address
buses, data buses and bus control signals ( RD and WR ) in a state of high impedance.
(The internal pull-up is enabled for the
external memory bus width, two or more bus cycles can occur in response to a single data
transfer (bus sizing). In this case, the end of the last bus cycle is the break of external
bus cycles.
If access to external areas occurs consecutively on the TMP19A61, a dummy cycle can be
inserted. Again, requests for buses are accepted at the break of external bus cycles on
the internal buses (G-BUS). During a dummy cycle, the next external bus cycle is already
started on the internal buses. Therefore, even if the BUSRQ signal is asserted during a
dummy cycle, the bus is not released until the next external bus cycle is completed.
Keep asserting the BUSRQ signal until the bus control authority is released.
Fig. 8.19 shows the timing of acquiring bus control authority by the external bus master.
The external bus master can acquire control authority only for TMP19A61 external buses,
The external bus master requests the TMP19A61 for bus control authority by asserting the
Depending on the relationship between the size of data to be loaded or stored and the
BUSRQ signal. The TMP19A61 samples the BUSRQ signal at the break of external
TMP19A61(rev1.0)-8-217
R
/
W
, HWR and CSx .)
TMP19A61

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