PC7410 datasheet(44/54 Pages) ATMEL

44 / 54 page

PC7410

2141D–HIREL–02/04

During inactive periods on the bus, the address and transfer attributes may not be

driven by any master and may, therefore, float in the high-impedance state for relatively

long periods of time. Since the PC7410 must continually monitor these signals for

snooping, this float condition may cause excessive power draw by the input receivers on

the PC7410 or by other receivers in the system. These signals can be pulled up through

weak (10 k

Ω) pull-up resistors by the system, address bus driven mode can be enabled

(see the PC7410 RISC Microporcessor Family Users’ Manual for more information on

this mode), or these signals may be otherwise driven by the system during inactive peri-

ods of the bus to avoid this additional power draw. The snooped address and transfer

attribute inputs are: A[0:31], AP[0:3], TT[0:4], CI, WT, and GBL.

In systems where GBL is not connected and other devices may be asserting TS for a

snoopable transaction while not driving GBL to the processor, we recommend that a

strong (1 k

Ω) pull-up resistor be used on GBL. Note that the PC7410 will only snoop

transactions when GBL is asserted.

The data bus input receivers are normally turned off when no read operation is in

progress and, therefore, do not require pull-up resistors on the bus. Other data bus

receivers in the system, however, may require pull-ups, or that those signals be other-

wise driven by the system during inactive periods by the system. The data bus signals

are: DH[0:31], DL[0:31], and DP[0:7].

If address or data parity is not used by the system, and the respective parity checking is

disabled through HID0, the input receivers for those pins are disabled, and those pins

do not require pull-up resistors and should be left unconnected by the system. If parity

checking is disabled through HID0, and parity generation is not required by the PC7410

(note that the PC7410 always generates parity), then all parity pins may be left uncon-

nected by the system. The L2 interface does not normally require pull-up resistors.

PC7410 Datasheet(PDF) 44 Page - ATMEL Corporation