Hello everyone,

It is time for another hardware project: this time a serial interface

for the ZX81, 2068 and the SPECTRUM. The design is fully hardware

and software compatible with the popular TS2050 (TIMEX) modem.

As usual, I tried to keep the circuit as simple as possible to make

it easy to construct. I have build several of these units without problems.

This interface is suitable for transferring files to and from your PC (and

other computers). The hardware is self explanatory and easily constructed

using point to point solder connections on a perforated PCB. To simulate

a 2050, IO address 73 selects the data and address 77 the control register.

Install 0.1uF capacitors between the power pins of each chip. I used a DB25

connector but DB9 connectors may also be used. Although the RS232 circuit

is non-standard, it works well over short distances (3m) : add a level

converter if you like to meet the RS232 standard. To simplify connections

to other computers, I have installed a jumper (J1) on the DB25 connector

to tie CTS TO DSR and RTS leaving only the external connections for

RX,TX and GND. The TX and RX lines of this I/F must be connected to the

RX and TX lines respectively of the other unit.

Someone may suggest different connector arrangements, optimized for other

applications. I use a simple ML program to upload and download programs

at high speed from the PC found here. ZXUART.P

You may wish to use a communication program like the high resolution video

ZXTERM80 with build-in XMODEM. If you have any suggestions please post

them: feedback is vital for a project like this.

enjoy

wilf

TS 2050 MODEM COMPATIBLE SERIAL I/F

--------------------------------

74HC138 8251

+5V___________________________________________________

_______ | _______ | +| 10uF

| VCC|16_| | VCC|26_| ===

A5____________1|A | | | |

A6____________2|B Y3|12________11|CS | 0V

A7____________3|C | D0 ___27|D0 | DB25/9

A3____________4|E | D1 ___28|D1 | 74HC14

IORQ__________5|E | D2 ____1|D2 TXD|19__10_|\_9__[100]_____ 2/2

M1____________6|E | D3 ____2|D | |/ TX

| | D4 ____5|D4 |

| | D5 ____6|D5 | 74HC14

|_______| D6 ____7|D6 RXD|3___5__/|_6__[10K]______3/3

8| D7 ____8|D7 | \| | RX

0V | | [1M]

RD________________________________13|RD | |____7/5

WR________________________________10|WR | GND

A2________________________________12|C/D |

CLK_______________________________20|CLK |

| |

RESET________1_|\_2_______________21|RST |

|/ | |

* 74HC14 | |

| DTR|24___ not used

_______________ | |

5V__16| 74HC4060 Q5|5---o _25|RXC |

0V___8| | \__|__9|TXC | 74HC14

|_12|RST Q8|14--o | RTS|23___3_|\_4__[100]______4/7

|_______________| ** S1 | | |/ RTS

10| |11 | |

|--[10M]--| | CTS|17__13_/|_12_[10K]______5/8

| | XTAL = | | \| | CTS

|--]||[---| 4.9512MHz | | 74HC14 [1M]

| | | | |

33 === === 33 | | 0V

0V_______|_________|_______________4|VSS | 74HC14

| DSR|22__11_/|_10_[10K]______6/6

|_______| \| | DSR

[1M]

* 74HC14 PIN 14=5V PIN 7=0V

** S1 for BAUD rate selection

Q5=4915200Hz\32 divided internally by 16 or 64 = 9600/2400 baud

Q8=4915200Hz\256 divided internally by 16 or 64 = 1200/300 baud