SI2414 SILABS [Silicon Laboratories], SI2414 Datasheet - Page 19

• Manufacturer Part Number: SI2414
• Manufacturer: SILABS [Silicon Laboratories]

Parallel Interface
The parallel interface is an 8-bit data bus with a single
bit address. Figure 3 on page 10 shows the required
timing for the parallel interface.
If A0 = 0, the data bus represents a read/write to the
“Parallel Interface 0 (0x00)” register on page 65. If
A0 = 1, the data bus represents a read/write to the
“Parallel Interface 1 (0x01)” register on page 66).
The parallel port may be read/written by the host in
blocks by monitoring the receive/transmit FIFOs on the
Si2456/33/14. The transmit and receive FIFOs are 14
and 12 characters deep, respectively. The FIFOs can be
guaranteed to never fill/empty as long as TXE and RXF
are polled (and the TX/RX register is written/read
appropriately). The FIFOs can also be serviced on
interrupts by using the INT pin and setting the INTM
bit 3 in the “Parallel Interface 1 (0x01)” register.
Additionally, the CTS and the RTS bits are used to
control flow.
The INT pin in parallel mode operates differently than in
serial mode. In parallel mode, the pin is used primarily
to monitor and control the I/O FIFO. By default, the INT
function is triggered by a low-to-high transition on RXF,
TXE, or INT in the Parallel Interface 1 register. The INT
bit in the “Parallel Interface 1 (0x01)” register is set by
the events selected in U70. If the INTM bit is set, these
events cause a high-to-low transition on the INT pin.
Contact Silicon Labs Technical Support for detailed
parallel interface applications information.
Command Mode
Upon reset, the ISOmodem is in Command mode and
accepts “AT” commands. An outgoing modem call can
be made using the “ATDT#” (tone dial) or “ATDP#”
(pulse dial) command after the device is configured. If
the handshake is successful, the modem responds with
the response codes detailed in Table 16 on page 33.
The Si2456/33/14 does not enter Data mode until after
the protocol result code. In Data mode, “AT” commands
are not accepted. The Si2456/33/14 reverts to
Command mode if the modem connection is terminated.
However, there are three “escape” methods that may be
used to return the ISOmodem to Command mode from
Data mode. See I/O Control 0 (U70).
“+++”—The escape sequence is a sequence of three
escape characters that are set in S-register S2 (“+”
characters by default). If the ISOmodem detects the
“+++” sequence and detects no activity on the UART
before or after the “+++” sequence for a time period
set by S-register S12, it returns to Command mode.
This is enabled by setting U70[13] (TES) = 1
(default).
b
Rev. 0.9
The “ATO” command can be used to re-enter Data
mode no matter which “escape” method is used.
Flow Control
Flow control settings are configured with the “AT\Q”
commands. Possible settings are no flow control, CTS-
only flow control, RTS/CTS flow control, and XON/
XOFF. RTS is the flow control signal from the host.
When RTS is low, RXD serial transmission operates
normally. When RTS goes high, no more characters are
transmitted after the current character, and RXD is
clamped to mark (1). This state persists until RTS goes
low. Normal serial transmission resumes within one
character-time.
The CTS output pin controls flow from the Si2456/33/14
to the host. When CTS is low, the Si2456/33/14 is ready
to accept a character. While CTS is high, no data should
be sent to the Si2456/33/14 on TXD. Figure 2 on page 9
shows the timing for flow control and the serial interface.
The ISOmodem default setting configures it to
automatically retrain to a lower line rate depending on
line conditions. However, the UART speed remains
fixed as set by the “AT\Tn” command.
Data Mode
The Si2456/33/14 ISOmodem is in Data mode while it
has a telephone line connection to another modem or is
in the process of establishing a connection.
In Command and Data mode, the Si2456/33/14
operates in asynchronous mode only. Data protocols
are available to provide error correction to improve
reliability (V.42 and MNP2-4) and data compression to
increase throughput (V.42bis and MNP5).
Each connection between two modems in Data mode
begins with a handshaking sequence. During that
sequence, the modems determine the line speed, data
protocol, and related parameters for the data link.
Configuration through AT commands determines the
range of choices available to the modem in the
negotiation process. Most configuration options in the
Si2456/33/14 act to limit the range over which a
“ESC pin”—This feature is enabled by setting
U70[15] (HES) = 1
returns the modem to Command mode. In parallel
mode, the ESC pin is replaced functionally by the
ESC bit in the Parallel Interface 1 register. The ESC
pin is level-sensitive and should be left high until the
“OK/” result code indicates that the modem is in
Command mode.
“9th bit”—If 8-bit data format with escape is
programmed, a 1 detected on bit 9 returns the
modem to Command mode. (See Figure 2 on page
9.) This is enabled via the \B6 AT command.
Si2456/Si2433/Si2414
b
. A high level detected on this pin
19