CH1788ET 데이터 시트보기 (PDF) - Cermetek Microelectronics

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CH1788ET

Surface Mount PLCC 2400bps Modem

Cermetek Microelectronics 

Cermetek Microelectronics, Inc.

4. Cermetek recommends issuing the following setup

string ATS13=39S73=176<CR> for best

performance.

THE COMMAND FORMAT

Typical commands consist of three elements: the

attention sequence, the commands themselves, and

a terminating carriage return.

AT[commands]<CR>.

Where: AT represents attention sequence.

[Commands] represents command strings.

<CR> represents carriage return (ASCII 13

or HEX 0D).

Training the Modem. The CH1788 must be trained

to set the DTE speed (i.e., to match its host’s speed

and parity) so that the CH1788 is able to recognize

serial asynchronous commands sent to it by the

host’s UART. The host must retrain the CH1788

each time a reset is performed.

Modem Training Command Sequence. The

CH1788 is trained by sending it the AT sequence:

Enter: AT<CR>

Result: OK

Where: A and T may be either upper or lower case

but must be the same case.

<CR> represents carriage return

The AT sequence is referred to as the attention

sequence. When received, the CH1788 will respond

with one of the following status messages, depending

on whether the CH1788 is optioned for Terse

(abbreviated) or Verbose (English) status messages.

Result:

Result:

Where:

0<CR>

(Terse)

or

<CR><LF>OK<CR><LF> (Verbose)

<CR> represents carriage return (ASCII 13

or HEX 0D).

<LF> represents line feed (ASCII 10 or

HEX 0A).

After responding, the CH1788 will be in command

mode and ready to accept additional commands. An

alternate attention sequence A/ may be sent. This

command causes the previously entered command

string specified with the AT prefix to be executed.

AT Command Set. The available commands are

summarized in Table 5. Note that each command

may have several options and the options may be

influenced by various S-Register values. It is

recommended that the designer review Cermetek

publication CH1788 AT Commands and S-Registers

Reference Guide.

CH1788 Surface Mount PLCC 2400bps Modem

AT Command Structure. When issuing commands

to the CH1788, the backspace character-control-H

(ASCII 8 or HEX 08) may be used to perform

character editing.

Multiple commands may be placed on the command

line as long as the command line does not exceed 63

characters, excluding the letters AT. By way of

example, the command string below instructs the

CH1788 to configure itself to suppress character

echoing when in command mode E0 and then put

itself in the answer state A.

Enter: ATE0A<CR>

Result: OK

MODEM STATES

The CH1788 is in either of two states: command

mode or data mode. The CH1788 will only respond

to AT commands when it is in command mode.

When the modem is idle, by default it is in command

mode.

When data transmission is in progress, the CH1788 is

in data mode and will not recognize/respond to AT

commands. To cause the CH1788 to recognize

commands when in data mode, the host must send

an escape sequence to the CH1788 forcing the

CH1788 out of data mode and into command mode.

Only then will the CH1788 respond to AT commands.

If the CH1788 is Off-Hook, connected to a remote

modem and placed in command mode by its host, the

CH1788 will not transmit any commands received

from its host to the remote modem. However, when

in this state, the CH1788 will not receive data from

the remote modem.

Result Codes. After execution of an AT command

and at the completion of each dial attempt, the

CH1788 will deliver a status message on RXD.

Referring to Table 3, the message can be a Terse

(numeric) or Verbose (English) message. The

message type is controlled via the V command.

Various combinations of the listed result codes can

be selected with the W and X commands.

Escape Sequence. The escape sequence consists

of a “guard time” of one second (a period where no

characters are sent to the modem), followed by 3

escape characters (typically +++), followed by

another guard time of one second. The escape

character code is set in register S2. by default, the

escape character is set as “+.” There is no required

delay between characters. When the escape

sequence has successfully been sent, the escape

characters will not be transmitted to the remote

modem.

2003 Cermetek Microelectronics, Inc.

Page 8

Document No. 607-0018 Revision A2 (07/03)

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