Z86C21 datasheet(10/35 Pages) ZILOG

10 / 35 page

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Z86C21 MCU

WITH

8K ROM

PIN FUNCTIONS (Continued)

Port 3 (P37-P30). Port 3 is an 8-bit, CMOS compatible four-

fixed-input and four-fixed-output port. These eight I/O lines

have four-fixed input (P33-P30) and four fixed output

(P37-P34) ports. Port 3, when used as serial I/O, is pro-

grammed as serial in and serial out, respectively (Figure 8

and Table 4) Port 3 pins have Auto Latches only.

Port 3 is configured under software control to provide the

following control functions: handshake for Ports 0 and 2

(/DAV and RDY); four external interrupt request signals

(IRQ3-IRQ0); timer input and output signals (T

IN and TOUT),

and Data Memory Select (/DM).

UART Operation. Port 3 lines P30 and P37, are be pro-

grammed as serial I/O lines for full-duplex serial asynchro-

Out

PAD

Z86C21

MCU

Port 3

(I/O or Control)

Auto Latch

≈ 500 KΩ

PAD

Port 3 Output Configuration

Port 3 Input Configuration

Figure 8. Port 3 Configuration

nous receiver/transmitter operation. The bit rate is con-

trolled by the Counter/Timer0.

The Z86C21 automatically adds a start bit and two stop bits

to transmitted data (Figure 9). Odd parity is also available

as an option. Eight data bits are always transmitted,

regardless of parity selection. If parity is enabled, the

eighth bit is the odd parity bit. An interrupt request (IRQ4)

is generated on all transmitted characters.

Received data must have a start bit, eight data bits and at

least one stop bit. If parity is on, bit 7 of the received data

is replaced by a parity error flag. Received characters

generate the IRQ3 interrupt request.

Z86C21 Datasheet(PDF) 10 Page - Zilog, Inc.

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