Propeller Manual

3: Assembly Language Reference – RDWORD
RDWORD
Instruction: Read word of main memory.
RDWORD Value, 〈#〉 Address
Result: Zero-extended word is stored in Value.
•
Value (d-field) is the register to store the zero-extended word value into.
•
Address (s-field) is a register or a 9-bit literal whose value is the main memory
address to read from.
Opcode Table:
–INSTR– ZCRI –CON– –DEST– –SRC– Z Result C Result Result Clocks
000001 001i 1111 ddddddddd sssssssss
Result = 0 --- Written 7..22
Concise Truth Table:
In Out
Destination Source Z C Effects Destination
1
Z
2
C
$----_----; - $----_----; - - -
wz wc 31:16 = 0, 15:0 = word value
0 0
1
Destination Out is the zero-extended word value read from main memory and is always generated since including an NR effect
would turn RDWORD into a WRWORD instruction.
2
The Z flag is cleared (0) unless Destination Out equals 0.
Explanation
RDWORD syncs to the Hub, reads the word of main memory at Address, zero-extends it, and
stores it into the Value register Address can point to any byte within the desired word; the
address’ lower bit will be cleared to zero resulting in an address pointing to a word boundary.
If the
WZ effect is specified, the Z flag will be set (1) if the value read from main memory is
zero. The
NR effect can not be used with RDWORD as that would change it to a WRWORD
instruction.
RDWORD is a hub instruction. Hub instructions require 7 to 22 clock cycles to execute
depending on the relation between the cog’s hub access window and the instruction’s moment
of execution. See Hub on page 24 for more information.
Propeller Manual v1.1 · Page 337