Data Bus (D15-D0); Data Transfer Acknowledge (Dtack); Dram Multiplexed Address Bus (Drama14-Drama0); Processor Function Codes (Fc2-Fc0) - Motorola MC68306 User Manual

BGACK can be negated (pulled high), and the MC68306 will operate in a two-wire bus
arbitration system.
2.1.7 Data Bus (D15–D0)
This bi-directional, three-state bus is the general-purpose data path. It is 16 bits wide and
can transfer and accept data of either word or byte length. During an interrupt
acknowledge cycle, an external device can supply the interrupt vector number on data
lines D7–D0.
2.1.8 Data Transfer Acknowledge (
Assertion of this bi-directional, open-drain signal indicates the completion of the data
transfer. When the processor recognizes DTACK during a read cycle, data is latched, and
the bus cycle is terminated. When DTACK is recognized during a write cycle, the bus
cycle is terminated. The MC68306 generates DTACK for all internal cycles, DRAM cycles,
and autovector IACK cycles, and can be programmed to generate DTACK for any chip
select cycle. (Refer to 3.7 Asynchronous Operation and 3.8 Synchronous Operation.)
2.1.9 DRAM Multiplexed Address Bus (DRAMA14–DRAMA0)
These signals provide fifteen multiplexed address bits used during row address strobe.
2.1.10 Processor Function Codes (FC2–FC0)
These function code outputs indicate the mode (user or supervisor) and the address
space type currently being accessed, as shown in Table 2-8. The function code outputs
are valid whenever AS is asserted.
HALT
2.1.11 Halt (
External assertion of this bi-directional signal causes the processor to stop bus activity at
the completion of the bus cycle for which the input met set-up time requirements (i.e.,
current or next cycle). This operation places all control signals in the inactive state. For
MOTOROLA

Table 2-8. Function Code Outputs

Function Code Output
FC2 FC1 FC0
Low Low Low
Low Low High
Low High Low
Low High High
High Low Low
High Low High
High High Low
High High High
)
MC68306 USER'S MANUAL
DTACK
)
Address Space Type
(Undefined, Reserved)
User Data
User Program
(Undefined, Reserved)
(Undefined, Reserved)
Supervisor Data
Supervisor Program
CPU Space
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