CHAPTER 2 PIN FUNCTIONS
User’s Manual U12688EJ4V0UM00
55
(9) P80 to P87 (Port 8) ··· 3-state I/O
Port 8 is an 8-bit input/output port that can be set to input or output in 1-bit units.
Besides functioning as a port, in the control mode it operates as a control signal output when memory and
peripheral I/O are externally expanded.
The operation mode can be set as port or control in 1-bit units, specified by the port 8 mode control register
(PMC8).
(a) Port mode
P80 to P87 can be set to input or output in bit units by the port 8 mode register (PM8).
(b) Control mode
P80 to P87 can be set in the port/control mode in bit units by the PMC8 register.
(i)
CS0 to CS7 (Chip Select) ··· 3-state output
This is the chip select signal for SRAM, external ROM, external peripheral I/O, page ROM and the
synchronous flash memory area.
The CSn signal is assigned to memory block n (n = 0 to 7).
It becomes active at the time the bus cycle when the corresponding memory block is accessed starts.
In the idle state (TI), it becomes inactive.
(ii) RAS0 to RAS7 (Row Address Strobe) ··· 3-state output
This is the strobe signal for the row address for the DRAM area and the strobe signal for the CBR
refresh cycle.
The RASn signal is assigned to memory block n (n = 0 to 7).
During on-page disable, after the DRAM access bus cycle ends, it becomes inactive.
During on-page enable, even after the DRAM access bus cycle ends, it is kept in the active state.
During the reset period and during a hold period, it is in the high impedance state, so connect it to
HV
DD
via a resistor.
(iii) IORD (I/O Read) ··· 3-state output
This is the read strobe signal for external I/O during DMA flyby transfer. It indicates whether the bus
cycle currently being executed is a read cycle for external I/O during flyby transfer, or a read cycle for
the SRAM area.
In order to make it possible to connect directly to memory or external I/O during DMA flyby transfer,
UWR or LWR rises before IORD rises.
Furthermore, this external I/O can be accessed even when it is assigned to the SRAM area.
Содержание V850E/MS1 UPD703100
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