MCP2200
1.3.4
HARDWARE FLOW CONTROL
TABLE 1-3:
Desired Rate
UART PRIMARY BAUD
RATES
Hardware flow control uses the RTS and CTS pins as
a handshake between two devices. The RTS pin of
one device is typically connected to the CTS of the
other device.
Actual rate
% Error
300
300
1200
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.16%
0.16%
0.16%
0.16%
0.16%
0.16%
1200
RTS is an active low output which notifies the other
device when it can receive data by driving the pin low.
The MCP2200 trip point for de-asserting RTS (high) is
63 characters. This is one character short of “buffer
full”.
2400
2400
4800
4800
9600
9600
19200
38400
57600
115200
230400
460800
921600
19200
38339
57692
115385
230769
461538
923077
CTS is an active low input which is used to notify the
MCP2200 when it can send data. The MCP2200 will
check CTS just before loading and sending UART data.
If the pin is asserted during a transfer, the transfer will
continue. Refer to Figure 1-1.
1.3.4.1
Flow Control Disabled
The buffer pointer does not increment (or reset to
zero) if the buffer is full. Therefore, if hardware flow
control is not enabled and an overflow occurs (i.e., 65
unprocessed characters received), the new data over-
writes the last position in the buffer.
1.4
USB Protocol Controller
The USB controller in the MCP2200 is full-speed USB
2.0 compliant.
• Composite device (CDC + HID):
FIGURE 1-1:
RTS/CTS CONNECTIONS
EXAMPLE
- CDC: USB-to-UART communications
- HID: I/O control, EEPROM access and initial
configuration
I am ready
to receive
I am ready
to receive
• 128 byte buffer to handle data throughput at any
UART baud rate:
RTS
RTS
- 64 byte transmit
- 64 byte receive
I’ll transmit
if okay
I’ll transmit
if okay
• Fully configurable VID and PID assignments, and
descriptors (stored on-chip)
CTS
CTS
MCU
MCP2200
• Bus powered or self-powered
1.4.1
DESCRIPTORS
EQUATION 1-1:
SOLVING FOR ACTUAL
BAUD RATE
The descriptors are stored in the MCP2200 during
configuration using the supplied PC interface.
12MHz
intx
ActualRate = ------------------
1.4.2
SUSPEND AND RESUME
Where:
The USB Suspend and Resume signals are supported
for power management of the MCP2200. The device
will enter Suspend mode when suspend signaling is
detected on the bus.
12MHz
x = ----------------------------------
DesiredBaud
The MCP2200 exits the Suspend mode when any of
the following occur:
1. Resume signaling is detected or generated
2. A USB Reset signal is detected
3. A device Reset occurs
2010 Microchip Technology Inc.
DS22228A-page 5
MICROCHIP [ MICROCHIP ]
