MCP2140_03 Datasheet, PDF (16/58 Pages) Microchip Technology – IrDA® Standard Protocol Stack Controller With Fixed 9600 Baud Communication Rate

MCP2140
2.10.1 IMPROVING THROUGHPUT
Actual maximum throughput is dependent on several
factors, including:
• Characteristics of the Primary device
• Characteristics of the MCP2140
• IrDA standard protocol overhead
The IrDA standard specifies how the data is passed
between the Primary device and Secondary device. In
IrCOMM, an additional 8 bytes are used by the protocol
for each packet transfer.
The most significant factor in data throughput is how
well the data frames are filled. If only 1 byte is sent at a
time, the throughput overhead of the IrCOMM protocol
is 89% (see Table 2-5). The best way to maximize
throughput is to align the amounts of data with the
receive buffer (IR and Host UART) packet size of the
MCP2140.
Then there is the delay between when data packets
are sent and received. See Figure 2-10 for an example
of this delay (look at CTS signal falling edges). In this
screen capture, a Palm™ m105 is receiving a 240-
byte string of data from the MCP2140. When the CTS
signal goes high, the Host Controller stops sending
data (23 bytes per CTS low-time). The CTS falling
edge to CTS falling edge is approximately 90 ms (typ-
ical). This CTS high-time affects the total data through-
put. The CTS high-time will be dependant on the
characteristics of the Primary device.
TABLE 2-5: IRCOMM OVERHEAD %
Data
Packet IrCOMM IrCOMM
Size Overhead Overhead
MCP2140 (Bytes) (Bytes) % ⁽¹⁾ Comment
IR
64
8
11 % Note 2
Receive ₁
8
89 %
Host
29
8
22 % Note 3
UART
23
8
26 % Note 4
Receive
1
8
89 %
Note 1: Overhead % =
Overhead/(Overhead + Data).
2: The maximum number of bytes of the IR
Receive buffer.
3: The maximum number of bytes of the
Host UART Receive buffer.
4: The CTS signal is driven high at 23 byte.
2.10.1.1 From the Primary Device
The MCP2140 uses a fixed IR Receiver data block size
of 64 bytes.
The minimum size frame the Primary device can
respond with is 6 bytes.
2.10.1.2 From the MCP2140
The MCP2140 uses a fixed Host UART Receiver data
block size of 29 bytes.
2.11 Turnaround Latency
An IR link can be compared to a one-wire data connec-
tion. The IR transceiver can transmit or receive, but not
both at the same time. A delay of one bit time is recom-
mended between the time a byte is received and
another byte is transmitted.
2.12 Device ID
The MCP2140 has a fixed Device ID. This Device ID is
“MCP2140 xx”, with the xx indicating the silicon
revision of the device.
DS21790A-page 16
Preliminary
 2003 Microchip Technology Inc.