Electronic Components Datasheet Search |
|
83C845 Datasheet(PDF) 11 Page - NXP Semiconductors |
|
83C845 Datasheet(HTML) 11 Page - NXP Semiconductors |
11 / 40 page 1996 Mar 22 11 Philips Semiconductors Product specification Microcontrollers for TV and video (MTV) 83C145; 83C845 83C055; 87C055 11 14-BIT PWM DAC (TDAC) 11.1 14-bit counter The 14-bit counter was already mentioned in Section 10. The nature of the counter is such that it can achieve a stable output value through its MSB, and the value can propagate through logic like that shown in Fig.5. The logic output can be stable within: • one period of the PWM clock (e.g. 250 ns) if edge-triggered logic is used to capture the logic output, or • one phase of the PWM clock (e.g. 125 ns) if a phase of the PWM clock is used to capture the logic output. The 14-bit (TDAC) counter is a ripple counter (cost and die-size reasons). The 14-bit PWM DAC is controlled by two special function registers TDACL and TDACH. 11.2 14-bit DAC operation When software wishes to change the 14-bit value (TD0 to TD13), it should first write to TDACL and then write to TDACH. Alternatively, if the required precision of the duty cycle is satisfied by 6 bits or less, software can simply write to TDACH (TD8 to TD13). 11.2.1 LOW PRECISION OPERATION Figure 5 shows that this block includes an ‘extra’ 14-bit latch between TDACL - TDACH and the comparator and other logic. The programmed value is clocked into the operative latch when the 7 low-order bits of the counter roll over to zero, provided that the software is not in the midst of loading a new 14-bit value, i.e. it is not between writing TDACL and writing TDACH. In a similar fashion to the lower-precision PWMs, this facility has an output flip-flop that is set when the lower 7 bits of the counter overflow/wrap. The more significant 7 bits of the operative latch’s programmed value are compared for equality against the less significant 7 bits of the counter, and the output FF is cleared when they match. Thus this output has a fixed period of 128 PWM clock cycles, and the duty cycle is determined by the programmed value. 11.2.2 HIGH PRECISION OPERATION For the higher-precision aspect of this feature, the 7 MSBs of the counter are used in a logic block with the 7 LSBs of the programmed value. The 7th LSB (binary value 64) of the programmed value is ANDed with the 7th MSB (128) of the counter, the 6th LSB of the value is ANDed with the counter’s 6th and 7th MSBs being 10, and so on through the LSB of the programmed value being ANDed with the counter’s 7 MSBs being 100000. Then these 7 ANDed terms are ORed. If the result is true (logic 1) at the time the 7 LSBs of the counter match the MSBs of the programmed value, the output is forced high for 1 (additional) PWM clock cycle. The result is that, if the value-64 bit of the 14-bit value is programmed to a logic 1, every other cycle of 128 PWM counter clocks has its duty cycle stretched by one counter clock; if the value-32 bit is programmed to logic 1, every 4th cycle is stretched, and so on through, if the value-1 bit is programmed to logic 1, one cycle out of each 128 is stretched. 11.2.3 14-BIT DAC OUTPUT Assuming the external integrator can handle all this, the net effect is a PWM DAC that has the period of a 7-bit design (which makes the integrator easier and more feasible to design) with the accuracy of a 14-bit one. An obvious prerequisite for such precision is that the load on the voltage must be very light, like a single op-amp or comparator. 11.2.3.1 Note The TDAC feature differs from the corresponding features of predecessor parts in several ways: 1. The 14-bit value is functionally composed of major and minor portions of 7 bits each. 2. The 14-bit value is programmed as a contiguous multi-register value that can be manipulated straight-forwardly via arithmetic instructions. 3. As discussed for the 6-bit DACs, both of the preceding parts had a feature whereby the PWM output could be inverted, redundantly with complementing the 14-bit value. This feature has been eliminated. |
Similar Part No. - 83C845 |
|
Similar Description - 83C845 |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.COM |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |