JPH04207230A - Semiconductor integrated circuit - Google Patents

Abstract

PURPOSE:To change the output synchronously with an event by constituting a D/A converter of plural registers, where digital values are stored, and a resistance ladder which converts output values from these registers to an analog voltage. CONSTITUTION:Transmission gates 1h, 1g, and 1f are opened in this order to write a digital value from a data bus 4 in registers 1e, 1b, and 1a in this order. Since a resistance ladder 2 generates an analog power corresponding to the value of a register 1c, the analog voltage corresponding to the first written digital value is outputted from an external output terminal 3. When an overflow signal 5b from a timer 5 is made effective, transmission gates 1d and 1e are opened, and the second written digital value is stored in the register 1c, and therefore, the analog voltage corresponding to this digital value is outputted from the external output terminal 3. When the overflow signal 5b is made effective again, the voltage corresponding to the third written digital value is outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor integrated circuit having a DA converter.

[Conventional technology]

Figure 2 is a block diagram of a D-A converter built into a conventional semiconductor integrated circuit. In the figure, (1) is a register that stores digital values, (2) is a resistance ladder, and (3) is an external output. The terminal (4) is a data bus.

Next, the operation will be explained. By writing a digital value from the data bus (4) into the register (1), an analog voltage corresponding to the value is generated from the resistance ladder (2) and output from the external output terminal (3).

[Problem to be solved by the invention]

Conventional semiconductor integrated circuits with built-in D-A converters are configured as described above, and the digital value to be converted to analog is stored in one register, so if you want to change the analog voltage, you need to use the register. There was a problem in that the value of had to be rewritten by software each time.

This invention was made in order to solve the above-mentioned problems, and it is possible to change the analog voltage without rewriting the value of the register each time by software - obtain a semiconductor integrated circuit with a built-in A converter The purpose is to

[Means to solve the problem]

A semiconductor integrated circuit according to the present invention includes a D-A converter configured with a plurality of registers that store digital values, and a resistance ladder that converts outputs from the plurality of registers into analog voltages, The output from the register is controlled so that the value written first is output first, and changes are made in synchronization with events such as timer overflow and external trigger signals.

[Effect]

In the semiconductor integrated circuit according to the present invention, the D-A converter is configured with a plurality of registers and a resistance ladder, so that the values of the registers can be easily rewritten without having to rewrite the values of the registers each time using software.
It becomes possible to change the analog voltage.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention in which three registers are used to store digital values, and the output from these registers is the timer auto 1 flow signal (D-
FIG. 2 is a block diagram of a converter.

In the figure, (1a) to (IC) are registers, (ld)
.

(1e) is a transmission gate that transmits the value of register (1a) to (1b) and the value of register (Ib') to (IC), and (1f) to (1h) transmit the value from data bus (4), respectively. This is a transmission gate that transmits information to the cash registers (1a) to (IC). (2) A resistor ladder that generates an analog voltage corresponding to the value of the IC, (3) an external output terminal that transmits the two analog voltages generated by the resistor ladder (2) to the outside, (5) A timer (5b) is an overflow signal of the timer (5) that counts the clock (5a) by a set value, and serves as a control signal for the transmission games h(ld) and (Ie).

The next self operation will be explained. 3 registers (1a)~
(IC), it is possible to store three digital values in advance, and by writing three times by software, the data node (4) and register (Ia) can be stored.
The transmission cable connected between ~ (IC) (Ih),
Open (Ig) and (If) in this order, and open the data node (4).
), the digital values from registers (Ic), (lb),
They are written in the order of (la). Since the resistor ladder (2) generates an analog voltage corresponding to the value of the register (Ic), the external output terminal (3) outputs an analog voltage corresponding to the first written digital value. Next, when the overflow signal 5b from the timer (5) becomes valid, the transmission gates (ld) and (Ie) open, and the values of the registers (la) and (Ib) change to (l), respectively.
b), (lc), and the register (IC) contains 2
Since the digital value written second is stored, an analog voltage corresponding to the digital value written second is output from the external output terminal (3). Furthermore, when the next overflow signal (5b) becomes valid, the same operation as above is performed and an analog voltage corresponding to the third written digital value is output from the external output terminal (3).

As shown above, input the three digital values into the register (
1a) to (Ic), and the digital value is changed by the timer overflow signal.
The analog voltage can be changed using software without having to rewrite register values one by one.

〔Effect of the invention〕

As described above, the present invention includes a plurality of registers storing the decimal JL value, which is controlled so that the value written first is output first, and the output changes in synchronization with an event; Since the D-A converter is constituted by a resistor ladder that converts the output from the register into an analog voltage, it has the effect that the analog voltage can be changed by software without rewriting the value of the register each time.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a DA converter according to an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional DA converter. In the figure, (Ia) to (Ic) are registers, (1d
) to (Ih) are transmission gates, (2) is resistance ladder, (3
) is the output terminal, (4) is the data bus, (5) is the timer,
(5a) shows the clock, and (5b) shows the overflow signal. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. 1st circuit Ci-T71i: Input great gate, 3: Output 1 addition Sa: Cloth 7 Sb, E8 70-1 symbol No. 2m Data bus procedure auxiliary device (spontaneous) 14:. == July 2, 1991

Claims (1)

[Claims] In a semiconductor integrated circuit having a D-A converter that converts a digital value into an analog voltage, the D-A converter has a plurality of registers that store digital values and converts output values from the plurality of registers into an analog voltage. The output from the plurality of registers is controlled so that the value written first is output first, and the output changes in synchronization with the event of the semiconductor integrated circuit. A semiconductor integrated circuit characterized by: