CHAPTER 4 BCU
Preliminary User’s Manual A14874EJ3V0UM
97
(6) Transfer response
The transfer response is indicated by the VMWAIT, VMAHLD, and VMLAST signals, which are output from the
bus slave (The signal names on the bus slave side are VSWAIT, VSAHLD, and VSLAST). These signals
become effective only while the VBCLK signal is low level.
Table 4-6. VMWAIT, VMAHLD, and VMLAST Signals
VMWAIT
VMAHLD
VMLAST
Explanation
0
0
0
Status when the current transfer is completed (ready status)
0
0
1
Last response (burst transfer last response status)
1
0
0
Wait response (wait status)
1
1
0
Maintains address and control signal (address hold status)
Other than the above
(Reserved for future function expansion)
Remark
0: low-level 1: high-level
Caution Once the VMAHLD signal becomes active (1), hold the active level (1) until the VMWAIT signal
becomes inactive (0).
It is not possible to return to the wait state from the address hold state during a bus cycle.
VMWAIT
VMAHLD
VMWAIT
VMAHLD
(7) Transfer direction
The bus master uses the VMWRITE signal to indicate the transfer direction. This signal outputs a high level
during write access.
(8) Data bus direction control
The VBDC signal is the data input (VBDI31 to VBDI0) control signal output pin. This signal outputs a high level
during read access.
The VBDV signal is the data output (VBDO31 to VBDO0) control signal output pin. This signal outputs a high
level during write access.
Table 4-7. VBDC and VBDV Signals
VBDC
VBDV
Explanation
0
1
Read access
1
0
Write access
Remark
0: low-level 1: high-level