Internal Logic
DISCON
DISCOE
DISCON#
pin
Figure 5-2. Disconnect Pin Logic
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).
DISCON#
EZ-USB
1500
To 3.3V regulator
J1
1
VCC
D-
D+
2
3
4
D-
D+
GND
USB-B
Figure 5-3. Typical Disconnect Circuit (DISCOE=1)
Page 5-12
Chapter 5. EZ-USB CPU
EZ-USB TRM v1.9
CYPRESS [ CYPRESS ]
