Compaq 850 manual AGP 2X Transfers, GNT Trdy

Chapter 4 System Support

AGP 2X Transfers

During AGP 2X transfers, clocking is basically the same as in 1X transfers except that the 66-MHz CLK signal is used to qualify only the control signals. The data bytes are latched by an additional strobe (AD_STBx) signal so that an 8-byte transfer occurs in one CLK cycle (Figure 4-6). The first four bytes (DnA) are latched by the receiving agent on the falling edge of AD_STBx and the second four bytes (DnB) are latched on the rising edge of AD_STBx.

T1 T2 T3 T4 T5 T6 T7

CLK

AD D1A D1B D2A D2B D3A D3B D4A D4B

AD_STBx
GNT-
TRDY-
ST0..2	00x	xxx	xxx	xxx	xxx	xxx

Figure 4-6.AGP 2X Data Transfer (Peak Transfer Rate: 532 MB/s)

AGP 4X Transfers

The AGP 4X transfer rate allows sixteen bytes of data to be transferred in one clock cycle. As in 2X transfers the 66-MHz CLK signal is used only for qualifying control signals while strobe signals are used to latch each 4-byte transfer on the AD lines. As shown in Figure 4-7, 4-byte block DnA is latched by the falling edge of AD_STBx while DnB is latched by the falling edge of AD_STBx-.

T1 T2 T3 T4

CLK

AD D1A D1B D2A D2B D3A D3B D4A D4B

AD_STBx

AD_STBx-

ST0..2 xxx 00x xxx xxx

Figure 4-7.AGP 4X Data Transfer (Peak Transfer Rate: 1064 MB/s)

4-12Compaq Deskpro EXS and Workstation 300 Personal Computers

Featuring the Intel Pentium 4 Processor

First Edition - December 2000