6821 datasheet, 6821 datasheets, 6821 pdf, 6821 circuit : MOTOROLA - PERIPHERAL INTERFACE ADAPTER ,alldatasheet, datasheet, Datasheet search site for Electronic ... Notes. Port A is designed to drive CMOS logic to normal 30%/70% levels. Port B uses three-state NMOS buffers and requires external resistors to pull up to CMOS levels. 40 pins = 51 x 12 mm 24 pins = 31 x 12 mm. 5101 RAM. 2716 EPROM. 6810 RAM. 6800 µProc. 6502 µProc. 6821 PIA Use a DMM and check for 4.5 volts at U8 pin 37 (6809), U27 pin 6 (6803), and U7 pin 34 (6821 PIA). If all are zero volts, the reset circuit is not working (all three chips should have their reset either high or low, if you have a mixed bag, there is a broken trace). The MC6808 is identical to the MC6802 except for on- board RAM. Since the MC6808 does not have on-board RAM pin 36 must be tied to ground allowing the processor to utilize up to WK bytes of external memory. The MPU has three 16-bit registers and three 8-bit registers available for use by the programmer (Figure 7).