Fujitsu MPB3021AT, Руководство по эксплуатации продукта

Страница: 78 / 180

C141-E045-02EN 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.