AT-command analyzing device

Details AT-command analyzing device AT-command analyzing device

2000-01-10

2004-03-09

Vo, Don N. (Department: 2631)

Pulse or digital communications

Transceivers

Modems

C375S225000, C375S369000, C375S370000, C375S296000, C375S243000, C375S140000, C375S140000

Reexamination Certificate

active

06704350

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for analyzing an AT command which is used in a modem device for personal computer.
2. Description of the Prior Art
The AT command used in a modem device for a personal computer in the prior art automatically recognizes and responds to a communication rate and a communication parameter between a DTE (Data Terminal Equipment) and a DCE (Data Circuit Terminating Equipment).
The AT command is such that the first two characters of the command are limited to ‘AT’ or ‘at’, and this is the reason why the AT command is called ‘AT’ command. What the AT command automatically recognizes and responds to is a communication rate and a communication parameter. An automatically recognizing method therefor will now be described.
Description will be made for the communication rate.
When ‘A’ or ‘a’ at the first of the command is expressed by ASCII code, ‘A’ and ‘a’ are expressed by 41h and 61h in hexadecimal notation, respectively. Because the least significant bit (LSB) of each of both is 1, a space (start bit) of one bit certainly appears at the beginning of the communication when each of both is converted into the LSB-first bit series of a serial interface. The communication rate is obtained as a result of measuring the time of this space.
In the times a personal-computer communication using the AT command started, the communication rate was 300 bps. However, the rate increases remarkably after that, to 14400 bps, then, 33600 bps, and, recently, 56000 bps is used. Moreover, the 56000 bps is the communication rate between a DCE and a DCE, and there is a possibility that data therebetween has been compressed to ¼ at the maximum. Therefore, for communication between a DCE and a DTE, it is necessary to satisfy the communication rate of 230.4 kbps which is the four times resulting from decompressing the thus compressed data. The standard baud rates used are 230400, 115200, 57600, 38400, 19200, 9600, 4800, 2400, 1200 and 300 bps. A difference in clock occurs between a transmission side and a reception side due to asynchronous communication. However, a frequency error of+2.5% through−1.0% is allowed with respect to a standard frequency at a rule. Therefore, when automatic setting of the rate is performed, it is necessary to detect a rate of reception from the other side, and set a frequency of a baud rate which is nearest to and supports this rate
Description will be made for the above-mentioned communication parameter.
With regard to the communication parameter, 8 bits (the start bit and 7 data bits) are set first without parity bit. The second character (T or t) is received at the communication rate obtained using the first character (A or a). Then, from a parity bit (D
7
) of each of the first character and second character and whether the characters are AT or at, the communication parameter which ITU-T, V.25ter supports is obtained.
FIG. 1
shows these communication parameters. D
7
which expresses the parity bit expresses the eighth bit when the respective bits are expressed by D
0
-D
7
in the LSB first manner, these respective bits comprising the 7 data bits and the following parity bit. The communication parameter is also called a data format.
The AT command has been analyzed using a microprocessor unit (MPU) in the prior art. However, because the communication rate has been increased as mentioned above and various functions have come to be used, the load of the MPU has increased. Japanese Laid-Open Patent Application No. 9-153923 discloses an art for reducing the load of the MPU and for automatic recognition of the communication rate using the AT command.
An AT-command analyzing device in the prior art disclosed in Japanese Laid-Open Patent Application No. 9-153923 is shown in
FIG. 2
, and will now be described.
In
FIG. 2
, RXD
100
is an input-data signal of a serial interface with a DTE. An analysis-commencement determining portion
101
receives instructions to start communication-rate analysis from a later-described MPU
109
, monitors the RXD
100
, and sends out a Start signal for rate-measurement commencement. A rate analyzing portion
102
receives the Start signal and analyzes the communication rate of the start bit. A serial-data control portion
103
prevents input of the RXD
100
to a later-described UART (Universal Asynchronous Receiver Transmitter)
108
during the period during which a gate signal output from the rate analyzing portion
102
is in the OFF state.
A decoder
104
generates rate data and frequency-dividing data for generating a baud-rate clock from a count value obtained as a result of the rate analyzing portion
102
counting clock pulses for the communication period of the start bit. A rate register
105
holds the rate data from the decoder
104
. A shift-register portion
106
including 8-bit shift register, receives the first character of the AT command, and holds it. A baud-rate clock generating portion
107
receives the frequency-dividing data from the decoder
104
, generates the baud-rate clock therefrom for receiving the command, and supplies it to the shift-register portion
106
and UART
108
. The UART
108
is a transmission and reception circuit which transmits and receives the RXD
100
which is asynchronous transmission serial data.
The MPU
109
outputs an indicate signal to the analysis-commencement determining portion
101
, and gives it the instructions to start communication-rate analysis. The MPU
109
receives the first character from the shift-register portion
106
, determines that it is ‘A’, receives received data starting from the second character and analyzes it. The analysis-commencement determining portion
101
determines that the ON state of the indicate signal from the MPU
109
is the instructions to start communication-rate analysis, and determines that no command has been provided, when a steady state in which the logic (H or 1) inverse to the logic (L or 0) of the start bit continues for more than ten periods of the shift-register clock (corresponding to the total 10 bits of the start, stop bits, parity bit and 7 data bits) in the RXD
100
which has been monitored. Then, the analysis-commencement determining portion
101
causes the Start signal to be in the ON state provided to the rate analyzing portion
102
, and causes it to start communication-rate analysis.
The rate analyzing portion
102
causes the gate signal to be in the OFF state, monitors the RXD
100
and waits for the start bit. The serial-data control portion
103
disconnects the UART
108
from the RXD
100
during the period during which the gate signal is in the OFF state, and, thereby, prevents the UART
108
from receiving the first character of the AT command at an erroneous communication rate before the rate is set. When the start bit appears in the RXD
100
, the rate analyzing portion
102
causes an internal counter to start, and measures the time of the start bit. Then, when the start bit finishes, the rate analyzing portion
102
causes the internal clock to stop, causes a load signal to be in the ON state, and provides a rate-measurement-completion interrupt signal to the MPU
109
.
The rate data includes the value of the rate calculated from the count value of the rate analyzing portion
102
and an error bit which is used, when the rate measurement has ended in failure, to report this matter. The rate register
105
holds the rate data from the decoder
104
at the time the load signal from the rate analyzing portion
102
comes to be in the ON state. The baud-rate-clock generating portion
107
loads therein the frequency-dividing data from the decoder
104
at the time the load signal from the rate analyzing portion
102
comes to be in the ON state, generates a new baud-rate clock based on this frequency dividing data, and supplies it to the UART
108
. Thereby, the UART
108
continually has the clock suitable to the communication rate supplied thereto. Further, the baud-rate-clock generating portion
107
supplies the sh

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