畢業(yè)設(shè)計(論文)外文資料翻譯〔含原文〕(編輯修改稿)
2025-07-16 17:30 本頁面
【文章內(nèi)容簡介】 l REQ64 is asserted by a 64bit bus master to indicate that is would like to perform 64bit data has the same timing and duration a s the FRAME signal. The REQ64 signal line must be supplied with a pull up resistor on the system cannot be permitted to float when a 32bit bus master is performing a transaction.l ACK64 is asserted by a target in response to REQ64 assertion by the master (if the target supports 64bit data transfers).ACK64 has the same timing and duration as DEVSEL(but ACK64 must not be asserted unless REQ64 is asserted by the initiator).Like REQ64,the AcK64 signal line must also be supplied with a pullup resistor on the system cannot be permitted to float when a 32bit device si the target of transaction.l AD [63::32] prise the upper four address/data paths.l C/BE [7::4] prise the upper four mand/byte enable signals.l PAR64 is the parity bit that provides even parity for the upper four AD paths and the upper four C/BE signal lines.The following sections provide a detailed discussion of 64bit data master and addressing capability.3． 64bit Cards in 32bit Addin Connectors A 64bit card installed in a 32bit expansion slot automatically only uses the lower half of the bus to perform transfers. This is true because the system board designer connects the REQ64 output pin and the ACK64 input pin on the connector to individual pullups on the system board and to nothing else. When a 64bit bus master is installed in a 32bit card slot and it initiates a transaction, its assertion of REQ64 is not visible to any of the target. In addition, its ACK64 input is always sampled deasserted (because it’s pulled up on the system board).This forces the bus master to use only the lower part of the bus during the transfer. Furthermore, if the target addressed in the transaction is a 64bit target, it samples REQ74 deasserted (because it’s pulled up on the system board),forcing it to only utilize the lower half of the bus during the transaction and to disable its ACK64 output. The 64bit extension signal lines on the card itself cannot be permitted to float when they are not in use. The CMOS input receives on the card would oscillate and draw excessive current, thus violating the “green” aspect of the specification. hen the card is installed in a 32 bit slot, it cannot use the upper half of the bus. The manner in which the card detects the type of slot (REQ64 sampled deasserted at startup time) is described in the next section.4． Pullups Prevent 64bit Extension from Floating When Not in Use If the 64bit extension signals
環(huán)評公示相關(guān)推薦
鄂ICP備17016276號-1