Fujitsu MPG3xxxAT, Product Manual

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C141-E110-02EN 5 - 13
5.2.3 Control block registers
(1) Alternate Status register (X'3F6')
The Alternate Status register contains the same information as the Status register of the command
block register.
The only difference from the Status register is that a read of this register does not imply Interrupt
Acknowledge and INTRQ signal is not reset.
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
BSY DRDY DF DSC DRQ 0 0 ERR
(2) Device Control register (X'3F6')
The Device Control register contains device interrupt and software reset.
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
X X X X X SRST nIEN 0
- Bit 2: SRST is the host software reset bit. When this bit is set, the device is held reset
state. When two device are daisy chained on the interface, setting this bit resets both
device simultaneously.
The slave device is not required to execute the DASP- handshake.
- Bit 1: nIEN bit enables an interrupt (INTRQ signal) from the device to the host. When this
bit is 0 and the device is selected, an interruption (INTRQ signal) can be enabled
through a tri-state buffer. When this bit is 1 or the device is not selected, the INTRQ
signal is in the high-impedance state.
5.3 Host Commands
The host system issues a command to the device by writing necessary parameters in related
registers in the command block and writing a command code in the Command register.
The device can accept the command when the BSY bit is 0 (the device is not in the busy status).
The host system can halt the uncompleted command execution only at execution of hardware or
software reset.
When the BSY bit is 1 or the DRQ bit is 1 (the device is requesting the data transfer) and the host
system writes to the command register, the correct device operation is not guaranteed.