CHAPTER 2 PIN FUNCTIONS
User’s Manual U13850EJ6V0UD
87
(9) P90 to P96 (Port 9) ··· 3-state I/O
P90 to P96 constitute a 7-bit I/O port that can be set to input or output pins in 1-bit units.
P90 to P96 can also function as control signal output pins and bus hold control signal output pins when memory
is expanded externally.
During 8-bit access of port 9, the highest bit is ignored during a write operation and is read as a “0” during a read
operation.
The I/O signal level uses the bus interface power supply pins BV
DD
and BV
SS
as a reference.
(a) Port function
P90 to P96 can be set to input or output in 1-bit units using the port 9 mode register (PM9).
(b) Alternate functions (External expansion function)
P90 to P96 can be set to operate as control signal outputs for external memory expansion using the
memory expansion mode register (MM).
(i)
LBEN (Lower byte enable) ··· output
This is a lower byte enable signal output pin for the external 16-bit data bus. During byte access of
odd-numbered addresses, these pins are set as inactive (high level). The output changes in
synchronization with the rising edge of the clock in the T1 state of the bus cycle. When the timing sets
the bus cycle as inactive, the previous bus cycle’s address is retained.
(ii)
UBEN (Upper byte enable) ··· output
This is an upper byte enable signal output pin for the external 16-bit data bus. During byte access of
even-numbered addresses, these pins are set as inactive (high level). The output changes in
synchronization with the rising edge of the clock in the T1 state of the bus cycle. When the timing sets
the bus cycle as inactive, the previous bus cycle’s address is retained.
Access
UBEN
LBEN
AD0
Word access
0
0
0
Halfword access
0
0
0
Byte access
Even-numbered address
1
0
0
Odd-numbered address
0
1
1
(iii) R/W (Read/write status) ··· output
This is an output pin for the status signal pin that indicates whether the bus cycle is a read cycle or
write cycle during external access. High level is set during a read cycle and low level is set during a
write cycle. The output changes in synchronization with the rising edge of the clock in the T1 state of
the bus cycle. High level is set when the timing sets the bus cycle as inactive.
(iv) DSTB (Data strobe) ··· output
This is an output pin for the external data bus’s access strobe signal. Output becomes active (low
level) during the T2 and TW states of the bus cycle. Output becomes inactive (high level) when the
timing sets the bus cycle as inactive.
Содержание V850/SB1
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