
6-4
M32000D3FP User's Manual
EXTERNAL BUS INTERFACE
6.2 External bus interface related signals
The M32000D3FP has the following signals related to the external bus.
(1) Address (A8 to A30)
The M32000D3FP has a 24-bit address bus (A8 to A31) corresponding to a 16 MB address space.
Of these, A31 (the LSB) is not output externally. In write cycles, the validity of the two bytes output
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on the 16-bit data bus is indicated by BCH and/or BCL. In read cycles, the 16-bit data bus is always
read, however, only data in the valid byte position in the M32000D3FP is transferred.
The address pins are bidirectional. If the M32000D3FP is in the hold state and the internal DRAM
is accessed from an external bus master, the address signal is input from the system bus side. In
this case, A8 to A11 are ignored, however, from the viewpoint of device protection care should be
taken that they are not left open circuit.
(2) Space identifier (SID)
The space identifier is used to specify user space and I/O space (I/O pin).
user space: SID = "L"
I/O space:
SID = "H"
If the M32000D3FP is in the hold state and the internal DRAM is accessed from an external bus
master, the "L" level should be input to SID from the system bus side.
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(3) Byte control (BCH, BCL)
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Byte control signals indicate the byte position of valid data transferred of the external bus cycle. BCH
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corresponds to the MSB side (D0 to D7), and BCL corresponds to the LSB side (D8 to D15). During
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the bus read cycle, both BCH and BCL are an "L" level. During the bus write cycle, BCH and/or BCL
go to an "L" level depending on the bytes to be written. If the M32000D3FP is in the hold state and
the internal DRAM is accessed from an external bus master, the byte control signal is input from the
system bus side.
(4) Data bus (D0 to D15)
The M32000D3FP has a 16-bit data bus to access external devices. If the M32000D3FP is in the hold
state and the internal DRAM is accessed from an external bus master, the data bus is used as a data
I/O bus from the system bus side.
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(5) Bus start (BS)
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When the M32000D3FP drives the bus cycle to the system bus, an "L" level is output to BS at the
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start of the bus cycle. Also, for a burst transfer, the BS signal is output for each transfer cycle. The
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BS signal is not output when accessing internal resources such as the internal DRAM or internal I/O
registers.
(6) Bus status (ST)
The ST signal identifies whether the bus cycle the M32000D3FP is driving is an instruction fetch
cycle or an operand access cycle.
instruction fetch access
: ST = "L"
operand access
: ST = "H"
hold
: ST = high-impedance
idle
: ST = undefined