PIC18F4550ESOSQTP datasheet(192/430 Pages) MICROCHIP

192 / 430 page

PIC18F2455/2550/4455/4550

DS39632D-page 190

Preliminary

18.2

Setup for USB Control

When the SPP is configured for USB operation, data

can be clocked directly to and from the USB peripheral

without intervention of the microcontroller; thus, no

process time is required. Data is clocked into or out

from the SPP with endpoint (address) information first,

followed by one or more bytes of data, as shown in

Figure 18-5. This is ideal for applications that require

isochronous, large volume data movement.

The following steps are required to set up the SPP for

USB control:

Configure the SPP as desired, including wait

states and clocks.

Set the SPPOWN bit for USB ownership.

Set the buffer descriptor starting address

(BDnADRL:BDnADRH) to FFFFh.

Set the KEN bit (BDnSTAT<5>) so the buffer

descriptor is kept indefinitely by the SIE.

Set the INCDIS bit (BDnSTAT<4>) to disable

automatic buffer address increment.

Set the SPPEN bit to enable the module.

18.3

Setup for Microcontroller Control

The SPP can also act as a parallel port for the

microcontroller. In this mode, the SPPEPS register

(Register 18-3) provides status and address write

control. Data is written to and read from the SPPDATA

When

the

SPP

owned

the

microcontroller, the SPP clock is driven by the

instruction clock (FOSC/4).

The following steps are required to set up the SPP for

microcontroller operation:

Configure the SPP as desired, including wait

states and clocks.

Clear the SPPOWN bit.

Set SPPEN to enable the module.

18.3.1

SPP INTERRUPTS

When owned by the microcontroller core, control can

generate an interrupt to notify the application when

each read and write operation is completed. The

interrupt flag bit is SPPIF (PIR1<7>) and is enabled by

the SPPIE bit (PIE1<7>). Like all other microcontroller

level interrupts, it can be set to a low or high priority.

This is done with the SPPIP bit (IPR1<7>).

18.3.2

WRITING TO THE SPP

Once configured, writing to the SPP is performed by

writing to the SPPEPS and SPPDATA registers. If the

SPP is configured to clock out endpoint address infor-

mation with the data, writing to the SPPEPS register

initiates the address write cycle. Otherwise, the write is

started by writing the data to the SPPDATA register.

The SPPBUSY bit indicates the status of the address

and the data write cycles.

The following is an example write sequence:

Write the 4-bit address to the SPPEPS register.

The

SPP

automatically

starts

writing

the

address. If address write is not used, then skip

to step 3.

Monitor the SPPBUSY bit to determine when the

address has been sent. The duration depends

on the wait states.

Write the data to the SPPDATA register. The

SPP automatically starts writing the data.

Monitor the SPPBUSY bit to determine when the

data has been sent. The duration depends on

the wait states.

Go back to steps 1 or 3 to write a new address

or data.

FIGURE 18-5:

TRANSFER OF DATA BETWEEN USB SIE AND SPP

Note:

If a USB endpoint is configured to use the

SPP, the data transfer type of that

endpoint must be isochronous only.

Note:

The SPPBUSY bit should be polled to

make certain that successive writes to the

SPPEPS or SPPDATA registers do not

overrun the wait time due to the wait state

setting.

Byte 0

Byte 1

Byte 2

Byte 3

Byte n

Endpoint

Address

Write USB endpoint number to SPP

Write outbound USB data to SPP or

read inbound USB data from SPP

PIC18F4550ESOSQTP Datasheet(PDF) 192 Page - Microchip Technology

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