Page 156 - Making PIC Microcontroller Instruments and Controllers

FESOUFCE
i4a USING LlOUlD CBYSTAI OISPLAYST Ail EXTE T ED IIFOBI/|ATION

PIC PIN DESIGNATION
1 VSS llel esnne6l€d te the l'l€
? vDD I'lei€er1e€led lelhe Pl6
3 \'e lJ€l eenne€t€d te !h5 nle
4 RS ] RAz POITA
5 B W 2 F A 3
6 E 1 8
7 D B O 6

]O DB3
11 DB4
"
DB5 11 RBs ) Half lhe pon can also be use
'
BBo )See PBP manual
"
RB7 )
15 BE N6l6e1n€€tsd te th€ Plg
16 BL lt€t oenneotsd 16 ihe Pl€

Table 9.4 i ndicales that our mio ocontroller does not necd to be connected to lines I '
and nol rvith dala l/O
2. 3, 15, and 16 in thal thcse have lo do with powcr connecliorrs
ln the preccding case. wc will use an 8 bit data buss. and thc conneclion to the PIC
16F877Awill be as shown ir lJigure 9 1.
we can get by with ll lines, and possibly even l0 if we decjde to do withoul
the ability to read from the display nremory. This is not usually the case, however,
because thcre are ti cs when we need to sel lhis line high for reading the LCD'S
busy flag in ordef to minimize lhe time used by LCD rolrtines Nevcrtheless. \\'e
car add abolLi a 20-milliscconds delay io take carc ofthe busy time Wc also necd
to be able to rcad the displa, memory il we want to scroll the display up and have
acccss to what is on ciisPlay lines one and two Since this wouldbe true ibr all apPli
cations, rve have to stay wi!h the l1 lincs for 8-bil control (We nould not have 10
read !he display if we kepl lrack of what we had put in the display somewhere elsc
in thc emory.)
The cight daia lincs fonn a coD\'crient bylc. and we can assign onc of the Porls not
being used lbr anything else. This lcaves three lrnes: