![Motorola MPC8240 Скачать руководство пользователя страница 76](http://html.mh-extra.com/html/motorola/mpc8240/mpc8240_user-manual_243927076.webp)
2-8
MPC8240 Integrated Processor User’s Manual
Detailed Signal Descriptions
2.2.1.1 PCI Bus Request (REQ[4:0])—Input
The PCI bus request signals (REQ[4:0]) are inputs on the MPC8240, and they have a
different meaning depending on whether the MPC8240 PCI arbiter is enabled or disabled.
The PCI REQn signals are point-to-point, and every master has its own REQn signal.
2.2.1.1.1 PCI Bus Request (REQ[4:0])—Internal Arbiter Enabled
The MPC8240 PCI arbiter is enabled by a low value on the reset configuration pin MAA2
or by the setting of bit 15 of the PCI arbitration control register. In this case, the REQ[4:0]
signals are used in conjunction with the GNT[4:0] signals as the arbiter for up to five PCI
masters. Following is the state meaning for the REQ[4:0] input signals in this case.
State Meaning
Asserted—External devices are requesting control of the PCI bus.
The MPC8240 acts on the requests as described in Section 7.2, “PCI
Bus Arbitration.”
Negated—Indicates that no external devices are requesting the use of
the PCI bus.
2.2.1.1.2 PCI Bus Request (REQ[4:0])—Internal Arbiter Disabled
The MPC8240 PCI arbiter is disabled by a high value on the reset configuration pin MAA2
or by the clearing of bit 15 of the PCI arbitration control register. In this case, the REQ0
becomes the PCI bus grant input for the MPC8240, and it is asserted when the external
arbiter is granting the use of the PCI bus to the MPC8240. Note that if the REQ0 input
signal is asserted prior to the need to run a PCI transaction, then the MPC8240 GNT0 signal
will not assert (the bus is parked) when a PCI transaction is to be run.
The REQ[4:1] input signals are ignored when the internal arbiter is disabled. Following is
the state meaning of the REQ0 signal when the internal arbiter is disabled.
State Meaning
Asserted—The REQ0 signal indicates that the MPC8240 is granted
control of the PCI bus. If REQ0 is asserted before the MPC8240 has
a transaction to perform (that is, the MPC8240 is parked), the
MPC8240 drives AD[31:0], C/BE[3:0], and PAR to stable (but
meaningless) states until they are needed for a legitimate transaction.
Negated—REQ0 is negated when the MPC8240 is not granted
control of the PCI bus.
2.2.1.2 PCI Bus Grant (GNT[4:0])—Output
The PCI bus grant (GNT[4:0]) signals are outputs on the MPC8240 and they have a
different meaning depending on whether the MPC8240 PCI arbiter is enabled or disabled.
The PCI GNTn signals are point-to-point; every master has its own GNTn signal.
2.2.1.2.1 PCI Bus Grant (GNT[4:0])—Internal Arbiter Enabled
The MPC8240 PCI arbiter is enabled by a low value on the reset configuration pin MAA2
or by the setting of bit 15 of the PCI arbitration control register. In this case, the GNT[4:0]
Содержание MPC8240
Страница 1: ...MPC8240UM D Rev 1 1 2001 MPC8240 Integrated Processor User s Manual ...
Страница 38: ...xviii MPC8240 Integrated Processor User s Manual TABLES Table Number Title Page Number ...
Страница 48: ...xlviii MPC8240 Integrated Processor User s Manual Acronyms and Abbreviations ...
Страница 312: ...6 94 MPC8240 Integrated Processor User s Manual ROM Flash Interface Operation ...
Страница 348: ...7 36 MPC8240 Integrated Processor User s Manual PCI Host and Agent Modes ...
Страница 372: ...8 24 MPC8240 Integrated Processor User s Manual DMA Register Descriptions ...
Страница 394: ...9 22 MPC8240 Integrated Processor User s Manual I2O Interface ...
Страница 412: ...10 18 MPC8240 Integrated Processor User s Manual Programming Guidelines ...
Страница 454: ...12 14 MPC8240 Integrated Processor User s Manual Internal Arbitration ...
Страница 466: ...13 12 MPC8240 Integrated Processor User s Manual Exception Latencies ...
Страница 516: ...16 14 Watchpoint Trigger Applications ...
Страница 538: ...B 16 MPC8240 Integrated Processor User s Manual Setting the Endian Mode of Operation ...
Страница 546: ...C 8 MPC8240 Integrated Processor User s Manual ...
Страница 640: ...INDEX Index 16 MPC8240 Integrated Processor User s Manual ...