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MCP2140A
DS22050B-page 16
2007-2011 Microchip Technology Inc.
2.10
Buffers and Throughput
The IR data rate of the MCP2140A is fixed at
9.6 kbaud. The actual throughput will be less due to
several factors. Many 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.
Depending on the application, throughput may be an
issue in one or both directions.
2.10.1
THROUGHPUT
Throughput is dependant on the direction that the data
is streaming and the characteristics of the primary
device and secondary device. Streaming throughput
from the secondary device may be different with differ-
ent primary devices. Also streaming throughput from
the secondary device may be different than streaming
throughput to the secondary device, with the same pri-
mary device. Throughput examples are shown in
observed data communications.
sequence between a primary device and a secondary
device (MCP2140A). In this example, after the “Primary
Device Sends Open Link Frame”, the time for the sec-
ondary device’s response is fixed by the operation of
the MCP2140A. After the “Primary Device Decodes
Secondary Device Response” the “Primary Device
Responds to Secondary Device”. Throughput may be
improved if the application program can be written so
that the primary device response is fast as possible.
Also, when the “Secondary Device Sends Data”, the
frame should have the maximum number of data bytes.
troller (and MCP2140A) streaming (transmitting) 250
bytes to a primary device (PIC24 + IrDA Standard Stack
Library).
(and host controller) receiving 250 streamed bytes from
a primary device (PIC24 + IrDA Standard Stack
Library).
controller (and MCP2140A) streaming (transmitting)
250 bytes to a primary device (PDA HP IPAQ H2495B).
controller (and MCP2140A) streaming (transmitting)
250 bytes to a primary device (PDA HP IPAQ H2495B).
TABLE 2-4:
THROUGHPUT EXAMPLES - 250 BYTES (3)
FIGURE 2-10:
HOST UART RECEIVE BUFFER AND CTS WAVEFORM
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
Primary Device
Secondary
Device
Data
Streaming
Direction
250 Byte
Transmit Time
(ms) (1)
Effective
Baud Rate (2)
Comment
PC (6)
MCP2140A (5)
S -> P
354
7062
Note 7
MCP2140
S -> P
650 (7)
3692
PIC IrDA Standard Stack (4) MCP2140A (5)
S -> P
337
7418
PIC IrDA Standard Stack (4) MCP2140A (5)
P -> S
549
4553
PDA (HP iPAQ hx2495b)
MCP2140A (5)
S -> P
332
7530
Note 1:
Measured from Figure. (see comment)
2:
Interpolated from Figure. (see comment)
3:
10 bits transferred for each byte.
4:
Using the PIC24 Explorer 16 Development Board with IR Transceiver Board
5:
Using the MCP215X/40 Data Logger Demo Board and Board Firmware V1.4
6:
IBM 600X Thinkpad (notebook computer) running Windows XP Professional (SP1)
7:
MCP2140 Data Sheet, DS21790, Table 2-4, MCP2140 transmitted 240 bytes in this transmit time.
CTS
Receive Buffer Empty
MCP2140A Can Receive Data
Receive Buffer Has 59 Bytes,
Receive Buffer
Receive Buffer Empty
MCP2140A Can Receive Data
IR Data Packet Transmitted
Full (60 Bytes)
CTS Pin Driven High
IR Data Packet Starts Transmission