Memory Controller
MPC885 PowerQUICC Family Reference Manual, Rev. 2
15-46
Freescale Semiconductor
15.6.4.6
Exception Pattern Entry (EXEN)
When the MPC885 under UPM control begins accessing a memory device, the external device may assert
TEA, SRESET, or HRESET. An exception occurs when one of these signals is asserted by an external
device and the MPC885 begins closing the memory cycle transfer. When one of these exceptions is
recognized and EXEN in the RAM word is set, the UPM branches to the special exception start address
(EXS) and begins operating as the pattern defined there specifies. See
Table 15-15
. The user should
provide an exception pattern to deassert signals controlled by the UPM in a controlled fashion. For DRAM
control, a handler should negate RAS and CAS to prevent data corruption. If EXEN = 0, exceptions are
deferred and execution continues. After the UPM branches to the exception start address, it continues
reading until the LAST bit is set in the RAM word.
15.6.4.7
Address Multiplexing (AMX)
To support many devices with multiplexed address signals, the upper address signals can be driven on the
lower address lines. MxMR[AMA] and MxMR[AMB] control which upper address signals are on which
lower address signals.
Note that this feature of internally multiplexing address signals should only be used in a system where the
MPC885 is the only external bus master. If other devices can be bus masters, address multiplexing must
be done in external logic. One of the UPM’s output signals can be used to control this external multiplexing
logic; GPL5 has been specifically enhanced for this. See the description of GPL5 in
Section 15.6.4.4,
“General-Purpose Signals (GxTx, G0x).”
ORx[SAM] and the AMX field of the RAM words determine when the multiplexing occurs. ORx[SAM]
controls address multiplexing for the first clock cycle. The AMX field in the RAM word determines the
multiplexing for subsequent clock cycles. As an address is driven off of the falling edge of GCLK1–50,
the address in a particular clock cycle is actually controlled by the previous RAM word, as shown in
Figure 15-43
.
The AMX field can be used to output the contents of MAR on the address signals.
Figure 15-43
shows
address multiplex timing.
Write burst cycle
WLFx
Periodic timer expired
TLFx
Table 15-17. M
x
MR Loop Field Usage (continued)
Request Serviced
Loop Field
Содержание PowerQUICC MPC870
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Страница 780: ...SCC Ethernet Mode MPC885 PowerQUICC Family Reference Manual Rev 2 27 24 Freescale Semiconductor ...
Страница 794: ...SCC Transparent Mode MPC885 PowerQUICC Family Reference Manual Rev 2 28 14 Freescale Semiconductor ...
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Страница 1090: ...UTOPIA Interface MPC885 PowerQUICC Family Reference Manual Rev 2 43 8 Freescale Semiconductor ...
Страница 1120: ...AAL2 Implementation MPC885 PowerQUICC Family Reference Manual Rev 2 44 30 Freescale Semiconductor ...
Страница 1162: ...Fast Ethernet Controller FEC MPC885 PowerQUICC Family Reference Manual Rev 2 45 40 Freescale Semiconductor ...
Страница 1172: ...SEC Lite Overview MPC885 PowerQUICC Family Reference Manual Rev 2 46 8 Freescale Semiconductor ...
Страница 1176: ...SEC Lite Address Map MPC885 PowerQUICC Family Reference Manual Rev 2 47 4 Freescale Semiconductor ...
Страница 1214: ...SEC Lite Execution Units MPC885 PowerQUICC Family Reference Manual Rev 2 48 38 Freescale Semiconductor ...
Страница 1312: ...Byte Ordering MPC885 PowerQUICC Family Reference Manual Rev 2 A 8 Freescale Semiconductor ...
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