MCP2140-IP datasheet(15/58 Pages) MICROCHIP

15 / 58 page

 2003 Microchip Technology Inc.

Preliminary

DS21790A-page 15

MCP2140

2.10

Buffers and Throughput

The IR data rate of the MCP2140 is fixed at 9.6 kbaud.

The actual throughput will be less due to several fac-

tors. The most significant factors are under the control

of the developer. One factor beyond the control of the

designer is the overhead associated with the IrDA

standard. A throughput example is shown in Table 2-4.

Figure 2-9 shows the CTS waveform, what the state of

the buffers can be and the operation of the Host UART

and IR interfaces.

Figure 2-10 shows the screen-capture of a Host Con-

troller transmitting 240 bytes. Data is not transmitted

after CTS goes high (so only a maximum of 23 bytes of

the 29 byte buffer are utilized). Between data packets,

the CTS time can vary, depending on the Primary

Device (see blue circled CTS pulse in Figure 2-10).

TABLE 2-4:

THROUGHPUT

FIGURE 2-9:

HOST UART RECEIVE BUFFER AND CTS WAVEFORM

FIGURE 2-10:

HOST CONTROLLER TRANSMISSION OF A 240 BYTE PACKET

Bytes

Transferred

(3)

Bytes/

CTS Low

Time (S)

Effective

Baud Rate

240

23 (max) (1) 0.810133

2962 (1)

240

0.6500

3692 (2)

Note 1: Measured from Figure 2-10.

2: Interpolated from Figure 2-10.

3: 10 bits transferred for each byte.

Note:

IrDA throughput is based on many factors

associated with characteristics of the Pri-

mary and Secondary devices. These char-

acteristics may cause your throughput to

be more or less than is shown in Table 2-4.

CTS

Receive Buffer Empty

MCP2140 Can Receive Data Receive Buffer Has 22 Bytes,

Receive Buffer

Receive Buffer Empty

MCP2140 Can Receive Data

IR Data Packet Transmitted

Full (29 Bytes)

CTS Pin Driven High

IR Data Packet Starts Transmission

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