Cirrus-logic AN83 Manuel d'utilisateur télécharger pdf (Page 34)

AN83

34 AN83REV3

Q20 := (Q20 * CS_EL_b) + (/CS_EL_b * SDATA)

Q21 := (Q21 * CS_EL_b) + (/CS_EL_b * Q20)

Q22 := (Q22 * CS_EL_b) + (/CS_EL_b * Q21)

Q23 := (Q23 * CS_EL_b) + (/CS_EL_b * Q22)

; Decode logic

EQUALL = (Q20:*:LA20) * (Q21:*:LA21) ; :*: -> Exclusive NOR operator

EQUALH = (Q22:*:LA22) * (Q23:*:LA23)

ADD_VALID = /RESET * CS_EL_b * ADD_VALID ; stay clear till any write

+ /RESET * /CS_EL_b ; Set when address write

+ /RESET * ADD_VALID ; Remain set until reset

CHIPSEL_b = RESET ; Get set at RESET

+ /ADD_VALID ; Remain set till address is valid

+ (/ALE * CHIPSEL_b ; Do not change when ALE is LOW

+ (ALE * /(EQUALL * EQUALH)) ; Clear during ALE if address matches

; When ALE is active; CS_b goes active if EQUAL[1:2] are true

; When ALE is inactive; previous state of CS_b is latched.

Figure 23. PAL Program

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Cirrus-logic AN83 Manuel d'utilisateur Page 34