Jameco-electronics Rabbit 3000 Manuel d'utilisateur Page 48

  • Télécharger
  • Ajouter à mon manuel
  • Imprimer
  • Page
    / 349
  • Table des matières
  • MARQUE LIVRES
  • Noté. / 5. Basé sur avis des utilisateurs
Vue de la page 47
Users Manual 39
3.3.8 Input/Output Instructions
The Rabbit uses an entirely different scheme for accessing input/output devices. Any
memory access instruction may be prefixed by one of two prefixes, one for internal I/O
space and one for external I/O space. When so prefixed, the memory instruction is turned
into an I/O instruction that accesses that I/O space at the I/O address specified by the 16-
bit memory address used. For example
IOI LD A,(0x85) ; loads A register with contents
; of internal I/O register at location 0x85.
LD IY,0x4000
IOE LD HL,(IY+5) ; get word from external I/O location 0x4005
By using the prefix approach, all the 16-bit memory access instructions are available for
reading and writing I/O locations. The memory mapping is bypassed when I/O operations
are executed.
I/O writes to the internal I/O registers require only two clocks, rather than the minimum of
three clocks required for writes to memory or external I/O devices.
Vue de la page 47
1 2 ... 43 44 45 46 47 48 49 50 51 52 53 ... 348 349

Commentaires sur ces manuels

Pas de commentaire