Atari 1040STE, Field Service Manual

Page: 16 / 81

11
Note. DO NOT SWITCH CLOCK SOURCE WHILE THE SYSTEM IS ACTIVE.
As a result the GPO is no longer available.
MONITOR INPUTS:
HSYNC TTL level, negative, 3.3k ohm.
VSYNC TTL level, negative, 3.3k ohm.
Monochrome Digital 1.0 Vpp, 75 ohm.
RGB Analog 0–1.0 Vpp, 75 ohm. Audio 1 Vpp, 1 k ohm.
Monitor
1 – Audio Out
2 – Composite Video
3 – External Clock Select (Pull
low
for
external
dock
on
pin
4)
4 – Monochrome
Monitor
Detect
(when
used
for GENLOCK becomes clock)
5 – Audio In
6 – Green
7 – Red
8 – +12 Volt Pullup
9 – Horizontal Sync
10 – Blue
11 – Monochrome
12 – Vertical Sync
13 – Ground
Figure 2–1: Monitor Ports
2.12 INPUT/OUTPUT SUBSYSTEMS
2.12.1 Musical Instrument Communication
The Musical Instrument Digital Interface (MIDI) allows the integration of the STE with
music synthesizers, sequencers, drum boxes and other devices possessing a MIDI
interface. High speed (31.25 kilobaud) asynchronous current loop serial
communication of keyboard and program information is provided by two ports, MIDI
OUT and MIDI IN (MIDI OUT also supports the optional MIDI THRU port). MIDI
specifies that data consist of 8 data bits preceded by one start bit and followed by
one stop bit.
Communication takes place via a 6850 ACIA. The CPU writes to the 6850 in
response to interrupts which are passed from the 6850 to the MFP interrupt