HP 3000 III Series Manual page 38

System/CPU Overview
Table 2-2. Main Memory Configurations
I-----l----·----------·---T------------~----
1 1 1
PCA's Required
1 1 1
1
Bank
1
System
1------1---1---1-------
1
No.
I
Word Capacity
1
MCL
1
SMA
I
FLI
1
Total
I I 1 1 1 1
1-------1----------------1--------1----1----1---------
1
2
1
128 K
1
1
1
1
1
1
1
3
1
4
1
256K
1
1
1
2
1
1
1
4
1
6
1
384 K
1
1
I
3
1
1
I
5
1
8
1
512K
1
1
I
4
I
1
I
6
1
12
1
768 K
1
2
I
6
1
1
I
9
1
16
1
1024 K
1
2
I
8
1
1
I
11
I I 1 I 1 1
2-13. PORT CONTROLLER/SELECTOR CHANNEL. The Port Controller and
Selector Channels are designed to operate with high-speed I/O
devices. The Port Controller contains the MCU logic required to
interface the Selector Channels with Main Memory via the CTL Bus
and also resolves priority conflicts between selector Channels
for accessing the CTL Bus. (Although the Port Controller contains
three selector channel ports, only two Selector Channels can be
installed in the computer system at one time.) Physically, the
Port Controller consists of one PeA and, as shown in tables 1-1
through 1-3, is conventionally installed in Card Cage No.3. De-
tailed discussions of the Port Controller and Selector Channel
are contained in Section VII.
Each Selector Channel can handle up to eight Device Controllers.
Unl ike the Mul tiplexer Cllannel which sw itches between D=vice Con-
troll~rs
on demand (based on hardware priority), the Selector
Channel uses only one Device Controller at a time and that Device
Controller monopolizes the channel until the device's I/O program
is complete. Thus, only one I/O program is current at a given
time for anyone Selector Channel. Also, the Selector Channel
directly accesses Main Memory for data and I/O program word
transfers rather than indirectly as the Multiplexer Channel does
through the lOP. Physically, each Selector Channel consists of
three PCA's and, as shown in tables 1-1 through 1-3, are conven-
tionally installed in Card Cage No.3 and Card Cage No.4 depend-
ing on the computer system model.
2-14. DEVICE CONTROLLERS. The computer system can handle up to
125 Device Controllers. Device Controllers provide the hardware
I/O linkage between the computer system and external I/O devices.
Primarily, a Device Controller translates programmed I/O commands
(from a MUltiplexer or selector Channel) or direct I/O commands
(from the lOP) into unique control signals required by its as-
sociated external I/O device (s). A Device Controller also gen-
erates the interrupts required by its associated I/O device(s)
and the interrupts required by direct or programmed commands.
2-6