FOR
FOR
enCoRe™ USB CY7C63722/23
CY7C63743
For Endpoint 0 Count Register, whenever the count updates from a SETUP or OUT transaction, the count register locks and
cannot be written by the CPU. Reading the register unlocks it. This prevents firmware from overwriting a status update on
incoming SETUP or OUT transactions before firmware has a chance to read the data.
15.0
USB Regulator Output
The VREG pin provides a regulated output for connecting the pull-up resistor required for USB operation. For USB, a 1.5-kΩ
resistor is connected between the D– pin and the VREG voltage, to indicate low-speed USB operation. Since the VREG output
has an internal series resistance of approximately 200Ω, the external pull-up resistor required is RPU (see Section 25.0).
The regulator output is placed in a high-impedance state at reset, and must be enabled by firmware by setting the VREG Enable
bit in the USB Status and Control Register (Figure 13-1). This simplifies the design of a combination PS/2-USB device, since the
USB pull-up resistor can be left in place during PS/2 operation without loading the PS/2 line. In this mode, the VREG pin can be
used as an input and its state can be read at port P2.0. Refer to Figure 12-8 for the Port 2 data register. This input has a TTL
threshold.
In suspend mode, the regulator is automatically disabled. If VREG Enable bit is set (Figure 13-1), the VREG pin is pulled up to
VCC with an internal 6.2-kΩ resistor. This holds the proper VOH state in suspend mode
Note that enabling the device for USB (by setting the Device Address Enable bit, Figure 14-1) activates the internal regulator,
even if the VREG Enable bit is cleared to 0. This insures proper USB signaling in the case where the VREG pin is used as an
input, and an external regulator is provided for the USB pull-up resistor. This also limits the swing on the D– and D+ pins to about
1V above the internal regulator voltage, so the Device Address Enable bit normally should only be set for USB operating modes.
The regulator output is only designed to provide current for the USB pull-up resistor. In addition, the output voltage at the VREG
pin is effectively disconnected when the CY7C637xx device transmits USB from the internal SIE. This means that the VREG pin
does not provide a stable voltage during transmits, although this does not affect USB signaling.
16.0
PS/2 Operation
The CY7C637xx parts are optimized for combination USB or PS/2 devices, through the following features:
1. USB D+ and D– lines can also be used for PS/2 SCLK and SDATA pins, respectively. With USB disabled, these lines can be
placed in a high-impedance state that will pull up to VCC. (Disable USB by clearing the Address Enable bit of the USB Device
Address Register, Figure 14-1).
2. An interrupt is provided to indicate a long LOW state on the SDATA pin. This eliminates the need to poll this pin to check for
PS/2 activity. Refer to Section 21.3 for more details.
3. Internal PS/2 pull-up resistors can be enabled on the SCLK and SDATA lines, so no GPIO pins are required for this task (bit
7, USB Status and Control Register, Figure 13-1).
4. The controlled slew rate outputs from these pins apply to both USB and PS/2 modes to minimize EMI.
5. The state of the SCLK and SDATA pins can be read, and can be individually driven LOW in an open drain mode. The pins are
read at bits [5:4] of Port 2, and are driven with the Control Bits [2:0] of the USB Status and Control Register.
6. The VREG pin can be placed into a high-impedance state, so that a USB pull-up resistor on the D–/SDATA pin will not interfere
with PS/2 operation (bit 6, USB Status and Control Register).
The PS/2 on-chip support circuitry is illustrated in Figure 16-1.
Document #: 38-08022 Rev. **
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