MCP2200 datasheet(5/34 Pages) MICROCHIP

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 2010 Microchip Technology Inc.

DS22228A-page 5

MCP2200

1.3.4

HARDWARE FLOW CONTROL

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.

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”.

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.

FIGURE 1-1:

RTS/CTS CONNECTIONS

EXAMPLE

EQUATION 1-1:

SOLVING FOR ACTUAL

BAUD RATE

1.4

USB Protocol Controller

The USB controller in the MCP2200 is full-speed USB

2.0 compliant.

• Composite device (CDC + HID):

- CDC: USB-to-UART communications

- HID: I/O control, EEPROM access and initial

configuration

• 128 byte buffer to handle data throughput at any

UART baud rate:

- 64 byte transmit

-64 byte receive

• Fully configurable VID and PID assignments, and

descriptors (stored on-chip)

• Bus powered or self-powered

1.4.1

DESCRIPTORS

The descriptors are stored in the MCP2200 during

configuration using the supplied PC interface.

1.4.2

SUSPEND AND RESUME

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.

The MCP2200 exits the Suspend mode when any of

the following occur:

Resume signaling is detected or generated

A USB Reset signal is detected

A device Reset occurs

RTS

CTS

I am ready

to receive

I’ll transmit

if okay

I am ready

to receive

I’ll transmit

if okay

MCU

MCP2200

ActualRate

12MHz

int x



------------------

Where:

12MHz

DesiredBaud

-----------------------------------

TABLE 1-3:

UART PRIMARY BAUD

RATES

Desired Rate

Actual rate

% Error

300

0.00%

1200

0.00%

2400

0.00%

4800

0.00%

9600

0.00%

19200

0.00%

38400

38339

0.16%

57600

57692

0.16%

115200

115385

0.16%

230400

230769

0.16%

460800

461538

0.16%

921600

923077

0.16%

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