
Fast AMBA Peripherals
12-43
GMS30C7201 Data Sheet
Figure 12-13: High Speed Serial Frame Format for IrDA Transmission (4.0Mbps)
The preamble, start, and stop flags are a mixture of symbols which contain either 0, 1,
or 2 pulses within the four time-slots. Symbols with 0 and 2 pulses are used to construct
flags since they represent invalid data bit pairings (one pulse required per symbol to
represent one of four bit pairs). The preamble contains sixteen repeated transmissions
of the four symbols: 1000 0000 1010 1000, the start flag contains one transmission of
eight symbols: 0000 1100 0000 1100 0110 0000 0110 0000, and the stop flag contains
one transmission of eight symbols: 0000 1100 0000 1100 0000 0110 0000 0110. The
address, control, data, and CRC-32 all use the standard 4PPM DDs described above.
Address Field
The 8-bit address field is used by a transmitter to target a select group of receivers
when multiple stations are connected to the same set of serial lines. The address
allows up to 255 stations to be uniquely addressed (00000000 to 11111110). The
global address (11111111) is use to broadcast messages to all stations. Serial port 1
contains an 8-bit register which is used to program a unique address for broadcast
recognition as well as a control bit to enable/disable the address match function. Note
that the address of received frames is stored in the receive buffer along with normal
data, and that it is transmitted and received starting with its LSB and ending with its
MSB.
Control Field
The IPC control field is 8-bits and is optional (as defined by the user). The FIr does not
provide any hardware decode support for the control byte, but instead treats all bytes
between the address and the CRC as data. Note that the control field is transmitted and
received starting with its LSB and ending with its MSB.
Data Field
The data field can be any length which is a multiple of 8-bits, from 0 to 2045 bytes. The
user determines the data field length according to the application requirements and
transmission characteristics of the target system. Usually a length is selected which
maximizes the amount of data which can be transmitted per frame, while allowing the
64
symbols
8 symbols
4 DDs
(8 bits)
4 DDs
(8 bits)
8180
DDs
max
(2045
bytes)
16 DDs
(32 bits)
8
symbols
Preamble
Start Flag
Address
Control
(optional)
Data
CRC-32
Stop
Flag
Start Flag
|0000|1100|0000|1100|0110|0000|0110|0000|
|0000|1100|0000|1100|0000|0110|0000|0110|
Stop
Flag
Preamble
|1000|0000|1010|1000|... repeated 16 times