Lucent Technologies USS-720 manual Registers, Preliminary Data Sheet, Rev, Instant USB, September

Preliminary Data Sheet, Rev. 5	USS-720	Instant USB
September 1999	USB-to-IEEE	1284 Bridge

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.

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

Each of the nine registers are described in detail in Tables 21—29.

Lucent Technologies Inc. 5-15