CY7C63310, CY7C638xx
19. USB/PS2 Transceiver
Although the USB transceiver has features to assist in interfacing to PS/2, these features are not controlled using these registers. The registers only control the USB interfacing features. PS/2 interfacing options are controlled by the D+ and D– GPIO Configuration register (See Table
19.1 USB Transceiver Configuration
Table 19-1. USB Transceiver Configure Register (USBXCR) [0x74] [R/W]
Bit # | 7 | 6 | 5 | 4 |
| 3 | 2 | 1 | 0 |
Field | USB Pull up |
|
|
| Reserved |
|
| USB Force State | |
| Enable |
|
|
|
|
|
|
|
|
Read/Write | R/W | – | – | – |
| – | – | – | R/W |
Default | 0 | 0 | 0 | 0 |
| 0 | 0 | 0 | 0 |
|
|
|
|
|
|
|
|
|
|
Bit 7: USB Pull up Enable
0 = Disable the pull up resistor on D–
1 = Enable the pull up resistor on
Bit [6:1]: Reserved
Bit 0: USB Force State
This bit allows the state of the USB IO pins D– and D+ to be forced to a state when USB is enabled.
0 = Disable USB Force State
1 = Enable USB Force State. Allows the D– and D+ pins to be controlled by P1.1 and P1.0 respectively when the USBIO is in USB mode. Refer to Table
Note The USB transceiver has a dedicated 3.3V regulator for USB signalling purposes and to provide for the 1.5K D– pull up. Unlike the other 3.3V regulator, this regulator cannot be controlled or accessed by firmware. When the device is suspended, this regulator is disabled along with the bandgap (which provides the reference voltage to the regulator) and the D– line is pulled up to 5V through an alternate 6.5K resistor. During wake up following a suspend, the band gap and the regulator are switched on in any order. Under an extremely rare case when the device wakes up following a bus reset condition and the volt- age regulator and the band gap turn on in that particular order, there is possibility of a glitch or low pulse occurring on the D– line. The host can misinterpret this as a deattach condition. This condition, although rare, is avoided by keeping the bandgap circuitry enabled during sleep. This is achieved by setting the ‘No Buzz’ bit, bit[5] in the OSC_CR0 register. This is an issue only if the device is put to sleep during a bus reset condition.
20. USB Serial Interface Engine (SIE)
The SIE allows the microcontroller to communicate with the USB host at low speed data rates (1.5 Mbps). The SIE simplifies the interface between the microcontroller and the USB by incorpo- rating hardware that handles the following USB bus activity independently of the microcontroller.
■Translate the encoded received data and format the data to be transmitted on the bus.
■CRC checking and generation. Flag the microcontroller if errors exist during transmission.
■Address checking. Ignore the transactions not addressed to the device.
■Send appropriate ACK/NAK/STALL handshakes.
■Token type identification (SETUP, IN, or OUT). Set the appropriate token bit after a valid token is received.
■Place valid received data in the appropriate endpoint FIFOs.
■Send and update the data toggle bit (Data1/0).
■Bit stuffing and unstuffing.
Firmware is required to handle the rest of the USB interface with the following tasks:
■Coordinate enumeration by decoding USB device requests.
■Fill and empty the FIFOs.
■Suspend and Resume coordination.
■Verify and select Data toggle values.
Document | Page 57 of 83 |
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