CHAPTER 2 PIN FUNCTIONS
User’s Manual U12688EJ4V0UM00
57
(v) RD (Read Strobe) ··· 3-state output
This strobe signal shows that the bus cycle currently being executed is a read cycle for the SRAM,
external ROM, external peripheral I/O, page ROM or synchronous flash memory area.
In the idle state (TI), it becomes inactive.
(vi) WE (Write Enable) ··· 3-state output
This signal shows that the bus cycle currently being executed is a write cycle for the SRAM area. In
the idle state (TI), it becomes inactive.
(vii) BCYST (Bus Cycle Start Timing) ··· 3-state output
This outputs a status signal showing the start of the bus cycle. It becomes active for 1 clock cycle
from the start of each cycle.
In the idle state (TI), it becomes inactive.
(viii) OE (Output Enable) ··· 3-state output
This signal shows that the bus cycle currently being executed is a read cycle for the DRAM area.
In the idle state (TI), it becomes inactive.
(ix) HLDAK (Hold Acknowledge) ··· output
In this mode, this pin is the output pin for the acknowledge signal that indicates high impedance
status for the address bus, data bus, and control bus when the V850E/MS1 receives a bus hold
request.
While this signal is active, the impedance of the address bus, data bus and control bus becomes high
and the bus mastership is transferred to the external bus master.
(x) HLDRQ (Hold Request) ··· input
In this mode, this pin is the input pin by which an external device requests the V850E/MS1 to release
the address bus, data bus, and control bus. This pin accepts asynchronous input for the CLKOUT
signal. When this pin is active, the address bus, data bus, and control bus are set to high
impedance. This occurs either when the V850E/MS1 completes execution of the current bus cycle or
immediately if no bus cycle is being executed, then the HLDAK signal is set as active and the bus is
released.
In order to make the bus hold state secure, keep the HLDRQ signal active until the HLDAK signal is
output.
Содержание V850E/MS1 UPD703100
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