![Infineon Technologies XC2200 User Manual Download Page 591](http://html1.mh-extra.com/html/infineon-technologies/xc2200/xc2200_user-manual_2055439591.webp)
XC2200 Derivatives
System Units (Vol. 1 of 2)
The External Bus Controller EBC
User’s Manual
9-7
V2.1, 2008-08
EBC_X8, V1.0d1
9.2.2
Bus Cycle Phases
This chapter provides a detail description of each phase of an external memory bus
access cycle.
9.2.2.1
A Phase - CS Change Phase
The A phase can take 0-3 clocks. It is used for tristating databus drivers from the
previous cycle (tristate wait states after chip select switch).
A phase cycles are not inserted at every access cycle, but only when changing the CS.
If an access using one CS (CSx) ends and the next access with a different CS (CSy) is
started, then A phase cycles are performed according to the bits set in the
first
CS
(CSx). This feature is used to optimize wait states with devices having a long turn-off
delay at their databus drivers, such as EPROMs and flash memories.
The A phase cycles are inserted while the addresses and ALE of the next cycle are
already applied.
If there are some idle cycles between two accesses, these clocks are taken into account
and the A phase is shortened accordingly. For example, if there are three tristate cycles
programmed and two idle cycles occur, then the A phase takes only one clock.
9.2.2.2
B Phase - Address Setup/ALE Phase
The B phase can take 1-2 clocks. It is used for addressing devices before giving a
command, and defines the length of time that ALE is active. In multiplexed bus mode,
the address is applied for latching.
9.2.2.3
C Phase - Delay Phase
The C phase is similar to the A an B phases but ALE is already low. It can take 0-3 clocks.
In multiplexed bus mode, the address is held in order to be latched safely. Phase C
cycles can be used to delay the command signals (RW delay).
9.2.2.4
D Phase - Write Data Setup/MUX Tristate Phase
The D phase can take 0-1 clocks. It is used to tristate the address on the multiplexed bus
when a read cycle is performed. For all write cycles, it is used to ensure that the data are
valid on the bus before the command is applied.
9.2.2.5
E Phase - RD/WR Command Phase
The E phase is the command or access phase, and takes 1-32 clocks. Read data are
fetched, write data are put onto the bus, and the command signals are active. Read data
are registered with the terminating clock of this phase.
The READY function lengthens this phase, too. READY-controlled access cycles may
have an unlimited cycle time.