CY7C68001
Document #: 38-08013 Rev. *H
Page 6 of 42
or 16- bit operation by an internal configuration bit, and an
Output Enable signal SLOE enables the data bus driver of the
selected width. The external master must ensure that the
output enable signal is inactive when writing data to the SX2.
The interface can operate either asynchronously where the
SLRD and SLWR signals act directly as strobes, or synchro-
nously where the SLRD and SLWR act as clock qualifiers. The
optional CS# signal will tristate the data bus and ignore SLRD,
SLWR, PKTEND.
The external master reads from OUT endpoints and writes to
IN endpoints, and reads from or writes to the command
interface.
3.7.2.2
Read: SLOE and SLRD
In synchronous mode, the FIFO pointer is incremented on
each rising edge of IFCLK while SLRD is asserted. In
asynchronous mode, the FIFO pointer is incremented on each
asserted-to-deasserted transition of SLRD.
SLOE is a data bus driver enable. When SLOE is asserted, the
data bus is driven by the SX2.
3.7.2.3
Write: SLWR
In synchronous mode, data on the FD bus is written to the
FIFO (and the FIFO pointer is incremented) on each rising
edge of IFCLK while SLWR is asserted. In asynchronous
mode, data on the FD bus is written to the FIFO (and the FIFO
pointer is incremented) on each asserted-to-deasserted
transition of SLWR.
3.7.2.4
PKTEND
PKTEND commits the current buffer to USB. To send a short
IN packet (one which has not been filled to max packet size
determined by the value of PL[X:0] in EPxPKTLENH/L), the
external master strobes the PKTEND pin.
All these interface signals have a default polarity of low. In
order to change the polarity of PKTEND pin, the master may
write to the POLAR register anytime. In order to switch the
polarity of the SLWR/SLRD/SLOE, the master must set the
appropriate bits 2, 3 and 4 respectively in the FIFOPINPOLAR
register located at XDATA space 0xE609. Please note that the
SX2 powers up with the polarities set to low. Section 7.3
provides further information on how to access this register
located at XDATA space.
3.7.3
IFCLK
The IFCLK pin can be configured to be either an input (default)
or an output interface clock. Bits IFCONFIG[7:4] define the
behavior of the interface clock. To use the SX2’s internally-
derived 30- or 48-MHz clock, set IFCONFIG.7 to 1 and set
IFCONFIG.6 to 0 (30 MHz) or to 1 (48 MHz). To use an exter-
nally supplied clock, set IFCONFIG.7=0 and drive the IFCLK
pin (5 MHz – 50 MHz). The input or output IFCLK signal can
be inverted by setting IFCONFIG.4=1.
3.7.4
FIFO Access
An external master can access the slave FIFOs either
asynchronously or synchronously:
• Asynchronous–SLRD, SLWR, and PKTEND pins are
strobes.
• Synchronous–SLRD, SLWR, and PKTEND pins are en-
ables for the IFCLK clock pin.
An external master accesses the FIFOs through the data bus,
FD [15:0]. This bus can be either 8- or 16-bits wide; the width
is selected via the WORDWIDE bit in the EPxPKTLENH/L
registers. The data bus is bidirectional, with its output drivers
controlled by the SLOE pin. The FIFOADR[2:0] pins select
which of the four FIFOs is connected to the FD [15:0] bus, or
if the command interface is selected.
3.7.5
FIFO Flag Pins Configuration
The FIFO flags are FLAGA, FLAGB, FLAGC, and FLAGD.
These FLAGx pins report the status of the FIFO selected by
the FIFOADR[2:0] pins. At reset, these pins are configured to
report the status of the following:
• FLAGA reports the status of the programmable flag.
• FLAGB reports the status of the full flag.
• FLAGC reports the status of the empty flag.
• FLAGD defaults to the CS# function.
The FIFO flags can either be indexed or fixed. Fixed flags
report the status of a particular FIFO regardless of the value
on the FIFOADR [2:0] pins. Indexed flags report the status of
the FIFO selected by the FIFOADR [2:0]pins.[4]
3.7.6
Default FIFO Programmable Flag Set-up
By default, FLAGA is the Programmable Flag (PF) for the
endpoint being pointed to by the FIFOADR[2:0] pins. For EP2
and EP4, the default endpoint configuration is BULK, OUT,
512, 2x, and the PF pin asserts when the entire FIFO has
greater than/equal to 512 bytes. For EP6 and EP8, the default
endpoint configuration is BULK, IN, 512, 2x, and the PF pin
asserts when the entire FIFO has less than/equal to 512 bytes.
In other words, EP6/8 report a half-empty state, and EP2/4
report a half-full state.
3.7.7
FIFO Programmable Flag (PF) Set-up
Each FIFO’s programmable-level flag (PF) asserts when the
FIFO reaches a user-defined fullness threshold. That
threshold is configured as follows:
1. For OUT packets: The threshold is stored in PFC12:0. The
PF is asserted when the number of bytes in the entire FIFO
is less than/equal to (DECIS = 0) or greater than/equal to
(DECIS = 1) the threshold.
2. For IN packets, with PKTSTAT = 1: The threshold is stored
in PFC9:0. The PF is asserted when the number of bytes
written into the current packet in the FIFO is less than/equal
to (DECIS = 0) or greater than/equal to (DECIS = 1) the
threshold.
3. For IN packets, with PKTSTAT = 0: The threshold is stored
in two parts: PKTS2:0 holds the number of committed pack-
ets, and PFC9:0 holds the number of bytes in the current
packet. The PF is asserted when the FIFO is at or less full
than (DECIS = 0), or at or more full than (DECIS = 1), the
threshold.
Note:
4.
In indexed mode, the value of the FLAGx pins is indeterminate except when addressing a FIFO (FIFOADR[2:0]={000,001,010,011}).
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