AN2131-DK001 Cypress Semiconductor Corp, AN2131-DK001 Datasheet - Page 87

• Manufacturer Part Number: AN2131-DK001
• Description: KIT EZ-USB DEVELOPMENT BOARD
• Manufacturer: Cypress Semiconductor Corp

Specifications of AN2131-DK001

• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: 428-1333

The logic for the DISCON and DISCOE bits is shown in Figure 5-2. To simulate a USB
disconnect, the 8051 writes the value 00001010 to USBCS. This floats the DISCON# pin,
and provides an internal DISCON signal to the USB core that causes it to perform discon-
nect housekeeping.
To re-connect to USB, the 8051 writes the value 00000110 to USBCS. This presents a
logic HI to the DISCON# pin, enables the output buffer, and sets the RENUM bit HI to
indicate that the 8051 (and not the USB core) is now in control for USB transfers. This
arrangement allows connecting the 1,500-ohm resistor directly between the DISCON# pin
and the USB D+ line (Figure 5-3).
Page 5-12
DISCON
DISCOE
Figure 5-3. Typical Disconnect Circuit (DISCOE=1)
To 3.3V regulator
USB-B
VCC
GND
D+
J1
D-
Figure 5-2. Disconnect Pin Logic
1
2
3
4
Chapter 5. EZ-USB CPU
Internal Logic
1500
DISCON#
D-
D+
EZ-USB
DISCON#
pin
EZ-USB TRM v1.9