IDE and Flash Media InterfaceMCF5253 Reference Manual, Rev. 1Freescale Semiconductor 13-3To support this bus set-up, a number of signals are available.• BUFENB1—active-low external buffer enable. This enable is always active when the CS0/CS4pin is active, and should enable a buffer going to the external boot Flash / ROM and any additionalmemories or controllers.• When CS0 is being used internally as the Chip Select for the boot ROM, the CS0/CS4 pin operateswith the CS4 settings, BUFENB1 settings then apply to CS4.• BUFENB2—active-low external buffer enable. This enable is always inactive when the CS0/CS4pin is active, and should enable a buffer for the IDE / SmartMedia Interface.• IDE_DIOR, IDE_DIOW—active-low IDE bus read and write strobe can also be used to implementa SmartMedia interface.• IDE_IORDY—active-high “ready” indication from IDE device to MCF5253.NOTEEither of the buffer enables can be programmed to be active on CS1 or CS2The extra bus signals, and their configuration are detailed in the following section.13.1.1 Buffer Enables BUFENB1, BUFENB2, and Associated LogicBuffer enables BUFENB1 and BUFENB2 allow a seamless interface to external bus buffers. The buffersare placed on the address and the data bus.Figure 13-2. Buffer Enables (BUFENB1 and BUFENB2)As shown in Figure 13-2, the buffer enables BUFENB1 and BUFENB2 will go active at time CSPREbefore the falling edge of the Chip Select signal, and continue to be active for a time CSPOST after therising edge of the chip select signal. The pre-drive time CSPRE is realized by delaying the falling edge ofthe select signal. If pre-drive time CSPRE is programmed non-zero, and internal ColdFire cycletermination is used, chip select length will be CSPRE shorter than the programmed length. Times CSPRE,CSPOST are the same for both BUFENB1 AND BUFENB2. Times CSPRE, CSPOST are independentlyprogrammable for every Chip Select.Buffer enable configuration is programmable using the IDE_CONFIG1 register.CSx_corebufenx_bcspreCS0, CS1,DIOR, DIOW, SRE, SWEcspostBUFENBxCSPRE CSPOST
