Name: Sinclair ZX Spectrum
Brand: Sinclair
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Chapter 6

Output port 247 ($F7 = xxx10xxx):

RX data (inverted data bit, 0=Idle)

Not used by RS232 (set to 0)

Input port 247 ($F7 = xxx10xxx):

Not used by RS232

TX data (inverted data bit, 0=Idle)

Note that in order to transmit data on the RX data line of the RS232 socket, it is first

necessary to set the Comms_Out bit of output port 239. This is required because in a

ZX Interface 1 the output circuitry is shared between the Network and RS232. Although

there is no network functionality provided by the SPECTRA interface, this mechanism

has been reproduced to ensure that its RS232 port operates identically to that found

on the ZX Interface 1. The other control signals, TX data, DTR and CTS operate

irrespective of the state of the Comms_Out bit. Note also that the RX data and TX data

bits use inverted values, i.e. to send a ‘1’ it is necessary to write a ‘0’ to the RX data line

and vice versa, and when receiving a ‘1’ the TX data line will read in as ‘0’ and vice

versa.

RS232 communication performed by the ZX Interface 1 ROM transmits data one byte

at a time. Each byte is wrapped with a simple frame to form a packet that consists of a

start bit, each data bit (least significant bit first), and finally two stop bits. The

transmission duration of each bit lasts for a specific length of time as defined by the

baud rate, which dictates the number of bits sent per second. The highest baud rate

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General

Processor	Zilog Z80A
Clock Speed	3.5 MHz
RAM	16KB or 48KB
ROM	16KB
Graphics	256 x 192 resolution
Sound	1-channel beeper
Storage	Cassette tape
Input	Keyboard
Power	9V DC
Release Year	1982
Display	TV via RF modulator
Ports	Expansion, RF
Colors	15 (8 colours with two levels of brightness each, plus black)