Semiconductor Group
6-84
1999-04-01
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.
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 k
Ω
load to 3.6 V and in high state above 2.8 V with a 15 k
Ω
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
µ
s 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.
D+
D-
1
0
TPWD
DPWDR.1
+
RPWD
DPWDR.0
0
1
Transmit
Data
Receive
Data
Pin
Pin
30
Ω
Ω
30
MCS03413
Содержание C541U
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