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74HC4060 14-stage binary ripple counter with oscillator

2016-08-31 07:47  
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there is one drawback of using these chips comparing to 8250 chips, as there is no Programmable Baud Rate Generator or any other means of changing speed for direct chip connection. Akthough there are Baud Rate Generator Chips such as the AY-5-8116, a more cheaper (and common) alternative is the 74HC4060 14-bit Binary Counter and Oscillator.The 74HC4060, being a 14 bit binary counter/divider only has pinouts for some of it's stages. Only Q4 to Q14 is available for use as they have external connections. This means higher Baud Rates cannot be obtained from common crystals, such as the 1.8432 Mhz and 2.4576 Mhz. The UART requires a clock rate 16 times higher than the Baud Rate you will be using. eg A baud rate of 9600 BPS requires an input clock frequency of 153.6 Khz. 74HC4060 Baud Rate Generator using a 74HC4060 

Output

1.8432Mhz

2.4546Mhz

Out 2

115.2 KBPS

153.6 KBPS

Q4

7200 BPS

9600 BPS

Q5

3600 BPS

4800 BPS

Q6

1800 BPS

2400 BPS

Q7

900 BPS

1200 BPS

Q8

450 BPS

600 BPS

Q9

225 BPS

300 BPS

Possible Baud Rates using a 74HC4060

   The 1.8432 Mhz crystal gives some unfamiliar Baud Rates. While many of these won't be accepted by terminal programs or some hardware, they are still acceptable if you write your own serial programs. For example the PC's baud rate divisor for 7200 BPS is 16, 3600 BPS is 32, 1800 BPS is 64 etc. If you require higher speeds, then yuo can connect the UART to the OUT2 pin. This connection utilizes the oscillator, but no frequency division is applied here. Using OUT2 with a 1.8432 Mhz crystal connected gives a baud rate of 115,200 BPS. The CMOS CDP6402 UART can handle up to 200 KBPS at 5 volts, however your MAX-232 may be limited to 120 KBPS, but is still within range.