These signals are various items used for the addressing of devices in Zorro III mode by bus masters either on the bus or from the local bus. The bus controller translates local bus signals (68030 protocol on the A3000) into Zorro III signals; masters are responsible for creating the appropriate signals via their own bus control logic. Read Enable (READ) Read enable for the bus; READ is asserted by the bus master during a bus cycle to indicate a read cycle, READ is negated to indicate a write cycle. READ is asserted at address time, prior to /FCS, for a full cycle, and prior to /MTCR for a short cycle. READ stays valid throughout the cycle; no latching required. Multiplexed Address Bus (A8-A31) These signals are driven by the bus master during address time, prior to the assertion of /FCS. Any responding slave must latch as many of these lines as it needs on the falling edge of /FCS, as they're tri-stated very shortly after /FCS goes low. These addresses always include all configuration address bits for normal cycles, and the cycle type information for Quick Interrupt cycles . Short Address Bus (A2-A7) These signals are driven by the bus master during address time, prior to the assertion of /FCS, for full cycles, and prior to the assertion of /MTCR for short cycles. They stay valid for the entire full or short cycle, and as such do not need to be latched by responding slaves. Memory Space (FC0-FC2) The memory space bits are an extension to the bus address, indicating which type of access is taking place. Zorro III PICs must pay close attention to valid memory space types, as the space type can change the type of the cycle driven by the current bus master. The encoding is the same as the valid Motorola function codes for normal accesses. These are driven at address time, and like the low short address, are valid for an entire short or full cycle. FC0 FC1 FC2 Address Space Type Z3 Response ------- --- ------- ---------- ----------- 0 0 0 Reserved None 0 0 1 User Data Spce Memory 0 1 0 User Program Space Memory 0 1 1 Reserved None 1 0 0 Reserved None 1 0 1 Supervisor Data Space Memory 1 1 0 Superviser Program Space Memory 1 1 1 CPU Space Interrupts Table K-1: Memory Space Type Codes Compatibility Cycle Strobe (/CCS) This is equivalent to the Zorro II address strobe, /AS . A Zorro III PIC doesn't use this for normal operation, but may use it during the autoconfiguration process if configuring at the Zorro II address. AUTOCONFIG cycles at $00E8xxxx always look like Zorro II cycles, though /FCS and the full Zorro III address is available, so a card can use either Zorro II or Zorro III addressing to start the cycle. However, using the /CCS strobe can save the designer the need to compare the upper 8 bits of the address. Data must be driven Zorro II style, though if the /DSn lines are respected for reads, /CINH is asserted, and /MTACK is negated, the resulting Zorro III cycle will fit within the expected Zorro II cycle generated by the bus controller. Yes, that should sound weird; it's based on the mapping of Zorro II vs. Zorro III signals, and of course the fact that /FCS always starts any cycle. Also note that a bus cycle with /CCS asserted and /FCS negated is always a Zorro II PIC-as-master cycle. Many Zorro III cards will instead configure at the alternate $FF00xxxx base address, fully in Zorro III mode, and thus completely ignore this signal. Full Cycle Strobe (/FCS) This is the standard Zorro III full cycle strobe. This is asserted by the bus master shortly after addresses are valid on the bus, and signals the start of any kind of Zorro III bus cycle. Shortly after this line is asserted, all the multiplexed addresses will go invalid, so in general, all slaves latch the bus address on the falling edge of /FCS. Also, /BGn line is negated for a Zorro III mastered cycle shortly after /FCS is asserted by the master.
[Back to Amiga Developer Docs]