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SN74ACT2440 Arkusz danych(PDF) 10 Page - Texas Instruments |
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SN74ACT2440 Arkusz danych(HTML) 10 Page - Texas Instruments |
10 / 33 page SN74ACT2440 NuBus ™ INTERFACE CONTROLLER SCHS010 – D3158, OCTOBER 1988 – REVISED JANUARY 1991 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 10 Table 2. Master Block-Transfer Function Table A5 A4 A3 A2 A1 A0 LOCTM1 LOCTM0 BLOCK SIZE TYPE OF CYCLE X X X L H L L H 2 Write X XL H H L L H 4 Write X LH H H L L H 8 Write L HH HH L L H 16 Write X X X L H L H H 2 Read X XL H H L H H 4 Read X LH H H L H H 8 Read L H H H H L H H 16 Read slave block-transfer cycles The ’ACT2440 can support slave block-transfer cycles with the addition of the ’ALS2442. The first responsibility of a slave during block transfers is to determine the type and size of the block transfer. This information is provided by the requesting master and must be decoded from the TMx lines and the A5–A0 address lines (as provided by the ’ACT2420s). See Table 3 for additional details. The slave interim acknowledge input (SIACK) generates the interim acknowledge cycles via TM0. The slave external request output (SEREQ) signals the local board when an interim acknowledge has occurred on the bus. Figure 14 shows the timing diagram of a typical slave block read. Figure 15 shows the timing diagram of a typical slave block write. The beginning of these cycles looks like any other slave cycle; SEREQ goes active (low), signaling the local board that another master is requesting the local board. On the first sample edge after SGNTA is taken active (low), the AEN buffer signal is driven low, enabling the NuBus ™ addresses onto the local board. The A0, A1, and TMx lines must be decoded as provided on the ’ALS2442 in order to generate a block-transfer signal (represented on the timing diagrams as BLOCK). When this signal goes active (high), it signals the local board that a block transfer has been requested. Decoding A5-A2 determines the number of words to be transferred. The final acknowledge cycle is generated by driving LACK low. Table 3. Slave Block-Transfer Decode Table A5 A4 A3 A2 A1 A0 NTM1 NTM0 BLOCK SIZE TYPE OF CYCLE X X X L H L H L 2 Write X XL H H L H L 4 Write X LH H H L H L 8 Write L HH HH L H L 16 Write X X X L H L L L 2 Read X XL H H L L L 4 Read X LH H H L L L 8 Read L H H H H L L L 16 Read |
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