4-8
SCSI and DMA Registers
Register: 0xFC03
Target Command (TC)
Read/Write
When connected as a target device, the Target Command register allows
the microcontroller to control the SCSI bus information transfer phase
and/or to assert REQ/ simply by writing this register. The Target Mode
bit (register 0xFC02, bit 6) must be set (1) for bus assertion to occur.
When connected as an initiator with DMA Mode true, if the phase lines
(I_O/, C_D/ and MSG/) do not match the phase bits in this register, a
phase mismatch interrupt is generated when REQ/ goes active. In order
to send data as an initiator, the Assert I_O/, Assert C_D/ and Assert
MSG/ bits must match the corresponding bits in the
register (
). The Assert REQ/ bit (bit 3) has no
meaning when the SYM53C040 is operating as an initiator.
LBS
Last Byte Sent
7
In initiator mode, the SCSI core uses this bit to determine
when the last byte of a DMA transfer is sent to the SCSI
bus. This flag is necessary since the End of DMA bit in
the
register only reflects when the
last byte was received from the DMA function.
R
Reserved
[6:4]
AREQ
Assert REQ/
3
AMSG
Assert MSG/
2
ACD
Assert C_D/
1
AIO
Assert I_O/
0
These bits, when read together, give the current SCSI
bus phase.
describes the SCSI bus phases that
correspond to all possible values of these bits.
7
6
4
3
2
1
0
LBS
R
AREQ
AMSG
ACD
AIO
Defaults:
0
0
0
0
0
0
0
0
Содержание Symbios SYM53C040
Страница 12: ...xii Preface...
Страница 90: ...4 18 SCSI and DMA Registers...
Страница 98: ...5 8 SFF 8067 Registers...
Страница 110: ...6 12 Two Wire Serial Registers...
Страница 126: ...7 16 Miscellaneous Registers...
Страница 160: ...8 34 System Registers...
Страница 184: ...9 24 Electrical Characteristics...
Страница 194: ...A 10 Register Summary...
Страница 214: ......