User manual

Utility-band BPSK 6.0 kbps PLM PICtail™ Plus Daughter Board User’s Guide
DS75019A-page 24 © 2011 Microchip Technology Inc.
When called, the modem API functions will claim and start to use the following
processor resources:
• One ADC module (default: ADC1)
• One ADC input (default: AN8)
• One optional DMA channel for the ADC servicing (default: DMA0)
• One timer to trigger the ADC conversion:
- Timer3 when ADC1 is selected
- Timer5 when ADC2 is selected
• One DMA interrupt vector/ADC and its triggering timer interrupt vector
• One to four Output Compare channels. Default:
- OC1 and OC2 when PWM2 modulator is selected
- OC1 through OC4 when PWM4 modulator is selected
• Timer2 and its interrupt vector as PWM time base
• The GPIO pin selected in the configuration for CS control (default: RF0)
The memory and MIPS requirements for the modem software for different baud rates
(with DMA and RAM-saving options enabled) are listed in Table 3-1.
TABLE 3-1: MEMORY AND MIPS REQUIREMENTS FOR THE MODEM
3.1.6 Developing Custom Applications
An application template has been provided to ease the development of customized
PLM applications. The application template can be downloaded from the Utility-
band BPSK 6.0 kbps PLM PICtail™ Plus Daughter Board web site at:
www.microchip.com/powerline.
By default, the software for the daughter board is designed to operate on a carrier
frequency of 72 kHz. However, if required, the software can be modified to operate at
a different carrier frequency. In this case, the following need to be taken into
consideration:
• The hardware provided in the kit is designed to operate at a carrier frequency of
72 kHz. Changing the carrier frequency in software will require modifications to
the hardware components, specifically the components that decide the filter cutoff
frequencies
• It is necessary for the carrier frequency to be an integral multiple of the baud rate:
Carrier frequency, F
C
= k * baud, k ϵ Integer
• Lower carrier frequencies result in lower maximum possible data rates
• Carrier frequency or baud rate changes outside the combinations provided in the
include file (
...\modem\bpsk\bpsk_filter.inc) will require recalculation of
digital filter coefficients
• Increasing carrier frequency increases the MIPS requirement for the modem soft-
ware. For this reason, the carrier frequency must be well within the CPU’s useful
performance limit. The modem software requires approximately 0.234 to 0.303
MIPS/kHz of carrier frequency
Baud Rate RAM (Bytes) Flash (Bytes) MIPS
1200 444 2709 18.4
2400 284 2709 18.4
4800 204 2709 18.6
6000 188 2709 18.7