CY7C9689
Pin Descriptions (continued)
Pin
70
Name
TXHALF
I/O Characteristics
Signal Description
Three-state TTL out- Transmit FIFO Half-full Status Flag.
put, changes following
TXCLK¦
When the Transmit FIFO is enabled (FIFOBYP is HIGH and CE is LOW)
TXHALF is asserted when the HOTLink Transmit FIFO is Š half full (128 char-
acters is half full). If a Transmit FIFO reset has been initiated (TXRST was
sampled asserted for a minimum of seven TXCLK cycles), TXHALF is asserted
to enforce the full/unavailable status of the Transmit FIFO during reset.
When the Transmit FIFO is bypassed (FIFOBYP is LOW), TXHALF remains
deasserted, having no logical function.
TXHALF is forced to the High-Z state only during a “full-chip” reset (i.e., while
RESET is LOW).
60
TXEMPTY
Three-state TTL out- Transmit FIFO Empty Status Flag.
put, changes following
When the Transmit FIFO is enabled (FIFOBYP is HIGH and CE is LOW),
TXCLK¦ or REFCLK¦
TXEMPTY is asserted when the HOTLink Transmit FIFO has no data to forward
to the encoder. If a Transmit FIFO reset has been initiated (TXRST was sampled
asserted for a minimum of seven TXCLK cycles), TXEMPTY is deasserted and
remains deasserted until the Transmit FIFO reset operation is complete.
When the Transmit FIFO is bypassed (FIFOBYP is LOW), TXEMPTY is assert-
ed to indicate that the transmitter can accept data. TXEMPTY is also used as
a BIST progress indicator when TXBISTEN is asserted.
When TXBISTEN is asserted LOW, TXEMPTY becomes the transmit BIST-loop
counter indicator (regardless of the logic state of FIFOBYP). In this mode
TXEMPTY is asserted for one TXCLK or REFCLK period at the end of each
transmitted BIST sequence.
NOTE:
During BIST operations, when the Transmit FIFO is enabled (FIFOBYP
is HIGH), it is necessary to keep TXCLK operating, even though no data is
loaded into the Transmit FIFO and TXEN is never asserted, to allow the
TXEMPTY flag to respond to the BIST state changes.
The asserted state of this output (HIGH or LOW) is determined by the state of
the EXTFIFO input. When EXTFIFO is LOW, TXEMPTY is active LOW. When
EXTFIFO is HIGH, TXEMPTY is active HIGH.
If CE is sampled asserted (LOW), TXEMPTY is driven to an active state. If CE
is sampled deasserted (HIGH), TXEMPTY is placed into a High-Z state.
Receive Path Signals
RXCLK
8
Bidirectional TTL clock Receive Clock.
Internal Pull-Up
When the Receive FIFO is enabled (FIFOBYPis HIGH), this clock is the Receive
interface input clock and is used to control Receive FIFO read and reset, oper-
ations. When the Receive FIFO is bypassed (FIFOBYP is LOW), this clock
becomes the recovered Receive PLL character clock output which runs contin-
uously at the character rate.
41, 43, RXDATA[7:0]
45, 47,
48, 53,
Three-state TTL out- Parallel Receive DATA Outputs.
put, changes following
When the decoder is enabled (ENCBYP is HIGH), the low-order eight bits of
the decoded DATA character are presented on the RXDATA[7:0] outputs.
COMMAND characters, when they are received, do not disturb these outputs.
When the decoder is bypassed, the low order eight bits of the non-decoded
character are presented on the RXDATA[7:0] outputs.
RXCLK¦
59,61
When the Receive FIFO is disabled (FIFOBYP is LOW), these outputs change
on the rising edge of the RXCLK output. When the Receive FIFO is enabled
(FIFOBYP is HIGH), these outputs change on the rising edge of RXCLK input.
RXEN is the three-state control for RXDATA[7:0].
6
CYPRESS [ CYPRESS ]
