C541U_99 Datasheet, PDF (129/192 Pages) Siemens Semiconductor Group – 8-BIT CMOS MICROCONTROLLER

On-Chip Peripheral Components
C541U
6.4.9 On-Chip USB Transceiver
The C541U provides on-chip receiver and transmitter circuitries which allows to connect the C541U
directly to the USB bus. The USB driver circuitry is shown in figure 6-35. The USB transceiver is
capable of transmitting and receiving serial date at full speed (12 MBits/s) and low speed (1.5 Mbit/
s) data rates. Transceiver and receiver can be separately disabled for power down mode operation.
A single ended zero error condition (D+ and D- both at low level) can be detected.
1
0
TPWD
DPWDR.1
Transmit
Data
Receive
Data
1
0
RPWD
DPWDR.0
30 Ω
D+
Pin
30 Ω
D-
Pin
+
MCS03413
Figure 6-35
USB On-chip Driver Circuitry
The USB driver circuitry is a differential output driver which drives the USB data signal onto the
cable of the USB bus. The static output swing of the transmitter is in low state below 0.3 V with a
1.5 kΩ load to 3.6 V and in high state above 2.8 V with a 15 kΩ load to V_SS. The driver outputs
support tri-state operation to achieve bi-directional half duplex operation (control bits RPWD and
TPWD). High impedance is also required to isolate the port from devices that are connected but
powered down. The driver tolerates a voltage on the signal pins of -0.5 V to 3.8 V with respect to
local ground reference without damage. This voltage is tolerated for 10.0 µs while the driver is
active and driving, When the driver is in its high impedance state it tolerates this condition an
indefinitely long time.
For a full speed USB connection the impedance of the USB driver must be between 29 Ω and 44 Ω.
The data line rise and fall times are between 4 ns and 20 ns, smoothly rising or falling (monotonic),
and are well matched to minimize RFI emissions and signal skew. Figure 6-35 shows how the full
speed driver is realized using two identical CMOS buffers. Figure 6-36 shows the full speed driver
signal waveforms.
Semiconductor Group
6-84
1999-04-01