Figure 2. Framer Block Diagram
The MC92053 implements four copies of the TC sublay-
er of the DAVIC asymmetrical FTTC PHY specification
for network devices. The MC92053 key functional
blocks are described in the paragraphs which follow.
Tx UTOPIA Interface
The Transmit UTOPIA interface accepts ATM cells from
the ATM layer according to the UTOPIA Level 2 speci-
fication. Each cell is stored in one of the four transmit
cell FIFO’s. This block uses TXCLK provided by the
ATM layer. The FIFO’s are used for rate adaptation be-
tween TXCLK (the UTOPIA interface clock) and the de-
Rx UTOPIA Interface
The receive UTOPIA interface reads ATM cells from the
four receive cell FIFO’s and transfers them to the ATM
layer according to the ATM Forum UTOPIA Level 2
specification. This block uses RXCLK provided by the
ATM layer. The FIFO is used for rate adaptation be-
tween RXCLK (the UTOPIA interface clock) and the de-
The microprocessor interface is an 8-bit generic slave
interface. It is used for initializing the internal registers
and reading status registers and counters.
The MC92053 provides JTAG boundary scan.
Each of the four framers performs the TC functions for
a single user. The blocks contained in a framer are
shown in Figure 2 and are described in the paragraphs
Tx Cell Functions
The transmit cell functions block reads ATM cells from
a transmit cell FIFO. If there are no cells available when
a downstream frame should be transmitted, the cell
functions block generates an idle cell. It calculates the
HEC value based on the ATM header of each cell and
inserts it in the fifth octet of the cell. This block also ran-
domizes the payload of the ATM cells according to
ITU-T Recommendation I.432.
A count of the cells transferred from the transmit cell
FIFO is maintained.
Data Link Insertion Block
The data link insertion block provides direct serial ac-
cess to the data link bytes of the downstream frame
headers. The data link stream for the downstream
frames is optionally inserted using an output clock pin
and an input data pin. The device ID to which the data
link stream is destined is programmable.