Very high impedance. Very high impedance. Unused inputs must 'Float' high to logic 1 if Unused inputs must be be connected to +Vs or 0V. Inputs cannot be unconnected. 1mA must Inputs connected to +Vs or 0V. reliably driven by 74LS outputs unless a be drawn out to hold Compatible with 74LS resistor is used (see below). them at logic 0. (TTL) outputs. give give give Can up to 16mA Can about 5mA Can about give Can about 20mA, (enough to light an (10mA with 9V supply), 20mA, enough to source enough to light an LED. light an LED. To enough to light an LED. LED), but only Outputs To switch larger switch larger To switch larger currents about 2mA. To switch currents use a currents use a transistor. use a larger currents use a transistor. transistor. transistor. One output can drive One output can drive up up to 50 CMOS, 74HC One output can drive up to 50 CMOS, 74HC or Fan-out to 10 74LS inputs or 50 or 74HCT inputs, but 74HCT inputs, but only 10 74LS inputs. 74HCT inputs. only one 74LS input. Maximum about 1MHz about 25MHz about 25MHz about 35MHz Frequency A few µW. A few µW. A few µW. A few mW of the chip itself Removing a chip from its holder If you need to remove a chip it can be gently ejected out of the holder with a flat-blade screwdriver. Now carefully lever up each end by inserting the screwdriver blade, between the chip and its holder, and gently twisting the screwdriver. Take care to start lifting at both ends before you attempt to remove the chip, otherwise you will bend and possibly break the pins. Building the Circuit Throughout these experiments we will use TTL chips to build circuits. The steps for wiring a circuit should be completed in the order described below:
Inputs Very high impedance. Unused inputs must be connected to +Vs or 0V. Inputs cannot be reliably driven by 74LS outputs unless a resistor is used (see below). Very high impedance. Unused inputs must be connected to +Vs or 0V. Compatible with 74LS (TTL) outputs. 'Float' high to logic 1 if unconnected. 1mA must be drawn out to hold them at logic 0. Outputs Can give about 5mA (10mA with 9V supply), enough to light an LED. To switch larger currents use a transistor. Can give about 20mA, enough to light an LED. To switch larger currents use a transistor. Can give about 20mA, enough to light an LED. To switch larger currents use a transistor. Can give up to 16mA (enough to light an LED), but source only about 2mA. To switch larger currents use a transistor. Fan-out One output can drive up to 50 CMOS, 74HC or 74HCT inputs, but only one 74LS input. One output can drive up to 50 CMOS, 74HC or 74HCT inputs, but only 10 74LS inputs. One output can drive up to 10 74LS inputs or 50 74HCT inputs. Maximum Frequency about 1MHz about 25MHz about 25MHz about 35MHz of the chip itself A few µW. A few µW. A few µW. A few mW Removing a chip from its holder If you need to remove a chip it can be gently ejected out of the holder with a flat-blade screwdriver. Now carefully lever up each end by inserting the screwdriver blade, between the chip and its holder, and gently twisting the screwdriver. Take care to start lifting at both ends before you attempt to remove the chip, otherwise you will bend and possibly break the pins. Building the Circuit Throughout these experiments we will use TTL chips to build circuits. The steps for wiring a circuit should be completed in the order described below:
dld_lab_mannual_template_2012..docx