GMS30C7201 Datasheet, PDF (198/352 Pages) Hynix Semiconductor – 60MHz operation frequency Low power consumption

Fast AMBA Peripherals
At any time after the transmission of sixteen preambles, the start flag may be received. The start
flag is eight symbols long. If any portion of the start flag does not match the standard encoding,
the receive logic signals a framing error and the receive logic once again begins to look for the
frame preamble.
Once the correct start flag is recognized, each subsequent grouping of four DDs is decoded into
a data byte, placed within a five byte temporary buffer which is used to prevent the CRC from
being placed within the receive buffer. When the temporary buffer is filled, data values are
pushed out one by one to the receive buffer. The first data byte of a frame is the address. If
receiver address matching is enabled, the received address is compared to the address
programmed in the address match value field in one of the control registers. If the two values
are equal or if the incoming address contains all ones, all subsequent data bytes including the
address byte are stored in the receive buffer. If the values do not match, the receiver logic does
not store any data in the receive buffer, ignores the remainder of the frame, and begins to search
for the next preamble. The second data byte of the frame can contain an optional control field
as defined by the user and must be decoded in software (There is no hardware support within
the FIr).
Frames can contain any amount of data in multiples of 8-bits up to a maximum of 2047 bytes
(including the address and control byte). The FIr does not limit frame size, thus it is the
responsibility of the user to check that the size of each incoming frame does not exceed the IrDA
protocol’s maximum allowed frame size.
When the receive buffer is filled, an interrupt or DMA transfer is signalled. If the data is not
removed quickly enough, an overrun error is signalled when the receive logic attempts to place
additional data into the full buffer. Once the buffer is full, all subsequent data bytes received are
lost while all buffer contents remain intact.
If any two sequential symbols within the data field do not contain pulses (are 0000), the frame
is aborted, the least recent or oldest byte within the temporary buffer is moved to the receive
buffer (the remaining four buffer entries are discarded), the end of frame (EOF) tag is set within
the same buffer entry where the last “good” byte of data resides, and the receiver logic begins
to search for the preamble. An abort also occurs if any data symbol containing 0011, 1010, 0101,
or 1001 occurs (invalid symbols which do not occur in the stop flag).
The receive logic continuously searches for the 8-symbol stop flag. Once it is recognized, the
last byte which was placed within the receive buffer is flagged as the last byte of the frame and
the data in the temporary buffer is removed and used as the 32-bit CRC value for the frame.
Instead of placing this in the receive buffer, the receive logic compares it to the CRC-32 value
which is continuously calculated using the incoming data stream. If they do not match, the last
byte which was placed within the receive buffer is also tagged with a CRC error. The CRC value
is not placed in the receive buffer.
If the user disables the FIr’s receiver during operation, reception of the current data byte is
stopped immediately, the serial shifter and receive buffer are cleared, and all clocks used by the
receive logic are automatically shut off to conserve power.
Transmit Operation
Before enabling the FIr for transmission, the user may either “prime” the transmit buffer by
filling it with data or allow service requests to cause the CPU or DMA to fill the buffer once the
FIr is enabled. Once enabled, the transmit logic issues a service request if its buffer is empty.
For each frame output, a minimum of sixteen preambles are transmitted. If data is not available
after the sixteenth preamble, additional preambles are output until a byte of valid data resides
within the bottom of the transmit buffer. The preambles are then followed by the start flag and
then the data from the transmit buffer. Four symbols (8 bits) are encoded at a time and then
loaded into a serial shift register. The contents are shifted out onto the transmit pin clocked by
the 8MHz baud clock. Note that the preamble, start and stop flags, and CRC value is
automatically transmitted, and need not be placed in the transmit buffer.
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GMS30C7201 Data Sheet