Intel 6 SERIES CHIPSET - DATASHEET 01-2011 - Cycle Type; Direction (CYCTYPE + DIR); Cycle Type Bit Definitions; Size; Transfer Size Bit Definition

Datasheet 131
Functional Description
5.4.1.3 Cycle Type / Direction (CYCTYPE + DIR)
The PCH always drives Bit 0 of this field to 0. Peripherals running bus master cycles
must also drive Bit 0 to 0. Table 5-9 shows the valid bit encodings.
5.4.1.4 Size
Bits[3:2] are reserved. The PCH always drives them to 00. Peripherals running bus
master cycles are also supposed to drive 00 for Bits 3:2; however, the PCH ignores
those bits. Bits[1:0] are encoded as listed in Table 5-10.
Table 5-9. Cycle Type Bit Definitions
Bits[3:2] Bit1 Definition
00 0 I/O Read
00 1 I/O Write
01 0 Memory Read
01 1 Memory Read
10 0 DMA Read
10 1 DMA Write
11 x
Reserved. If a peripheral performing a bus master cycle generates this
value, the PCH aborts the cycle.
Table 5-10. Transfer Size Bit Definition
Bits[1:0] Size
00 8-bit transfer (1 byte)
01 16-bit transfer (2 bytes)
10
Reserved. The PCH never drives this combination. If a peripheral running a bus
master cycle drives this combination, the PCH may abort the transfer.
11 32-bit transfer (4 bytes)