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CD80C86 Fiches technique(PDF) 10 Page - Intersil Corporation |
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CD80C86 Fiches technique(HTML) 10 Page - Intersil Corporation |
10 / 35 page 10 FN2957.3 January 9, 2009 edge of this pulse, a valid address and certain status information for the cycle may be latched. Status bits S0, S1 and S2 are used by the bus controller, in maximum mode, to identify the type of bus transaction according to Table 2. Status bits S3 through S7 are time multiplexed with high order address bits and the BHE signal, and are therefore valid during t2 through t4. S3 and S4 indicate which segment register (see “Instruction Set Summary” on page 31) was used for this bus cycle in forming the address, according to Table 3. S5 is a reflection of the PSW interrupt enable bit. S3 is always zero and S7 is a spare status bit. I/O Addressing In the 80C86, I/O operations can address up to a maximum of 64k I/O byte registers or 32k I/O word registers. The I/O address appears in the same format as the memory address on bus lines A15-A0. The address lines A19-A16 are zero in I/O operations. The variable I/O instructions which use register DX as a pointer have full address capability while the direct I/O instructions directly address one or two of the 256 I/O byte locations in page 0 of the I/O address space. I/O ports are addressed in the same manner as memory locations. Even addressed bytes are transferred on the D7-D0 bus lines and odd addressed bytes on D15-D8. Care must be taken to ensure that each register within an 8-bit peripheral located on the lower portion of the bus be addressed as even. TABLE 2. S2 S1 S0 CHARACTERISTICS 0 0 0 Interrupt 001 Read I/O 010 Write I/O 011 Halt 1 0 0 Instruction Fetch 1 0 1 Read Data from Memory 1 1 0 Write Data to Memory 1 1 1 Passive (No Bus Cycle) TABLE 3. S4 S3 CHARACTERISTICS 0 0 Alternate Data (Extra Segment) 01 Stack 1 0 Code or None 11 Data 80C86 |
Numéro de pièce similaire - CD80C86 |
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Description similaire - CD80C86 |
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