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Preliminary Data Sheet, Rev. 5 USS-720
Instant USB
September 1999 USB-to-
IEEE
1284 Bridge
Lucent Technologies Inc. 5-15
IEEE
1284 Port (continued)
Registers
Nine parallel port registers are available to the host.
They are read and written using the
GET_1284_REGISTER and SET_1284_REGISTER
vendor-specific commands described above. The
SET_1284_REGISTER writes a value into a particular
register. Writes may either affect the configuration of
the hardware or have a direct effect on parallel port
control lines. In the case of the EPP Registers, writes
initiate EPP write cycles on the parallel port.
The GET_1284_REGISTER returns seven register val-
ues: Status, Control, Extended Control, USS-720 Con-
trol, Data, EPP Address/Data, and USS-720 Setup
Registers, in that order (see 19). Register values can
also be read via the Interrupt pipe, which returns the
values of Status, Control, Extended Control, and USS-
720 Control Registers, in that order (see Table 20).
Reads may affect the contents of the registers in one of
two ways. Any register read clears any interrupt status
that may exist at the time of the read. Also, a read tar-
geting the EPP address or EPP Data Register will ini-
tiate the appropriate EPP read cycle on the parallel
port. The value returned will be the address or data
byte read from the peripheral as a result of that read
cycle.
Each of the nine registers are described in detail in
Tables 21—29.
Table 19. GET_1284_REGISTER Data
Byte Register Data
0 Status
1 Control
2 Extended Control
3 USS-720 Control
4 Data
5 EPP Address/Data
6 USS-720 Setup
Table 20. Interrupt Pipe Read Data
Byte Register Data
0 Status
1 Control
2 Extended Control
3 USS-720 Control