PA-RISC Visualize Workstation Universal Serial Bus



Comparing USB to Legacy
Attribute USB PS/2 HP-HIL Serial Parallel
Ports per host Open (2 typ.) 2 1 Open (2 typ.) 1…3 (1 Typ.)
Pin count
4 6 (4 used) 4 3…25 (9 typ.) 34
Cable segment length
5m ~4m 3m 50 ft., however 3m
Max. transparent
distance
30m ~4m ~45m Unlimited
w/repeaters
Unlimited
w/repeaters
Topology
Tiered Star Point-to-Point Daisy-Chain Point-to-Point Point-to-Point
Device-to-Device I/O?
No N/A No No No
Hot attach/detach
Yes NoNoNo No
Device power
Bus or Local Host or Local Host only Local or
Parasitic
Local or
Parasitic
Power available
100-500mA / port 1 A / port 1 A / system Pull-up Trickle Pull-up Trickle
Power management
Yes NoNoNo No
Devices/port controller
127 2 + eavesdrops 7 1 + eavesdrops 1 + eavesdrops
Device enumeration
All Keyboard and
Mouse only
Yes Rarely Sometimes
Peak transfer rate
12 Mbps ~12.5 Kbps 60 Kbps ~115 Kbps ~3 MB/s
(typ. < 1 MB)
Error control
CRC None None Per device None
Flow control
Packet re-try Clocked I/O Clocked I/O Unreliable Handshake