Difference between revisions of "Jump"
m (Protected "Jump" ([edit=autoconfirmed] (indefinite) [move=autoconfirmed] (indefinite)))
Latest revision as of 08:45, 4 December 2010
|CP1610 Clock Cycles||12|
|Output Flags||Interrupt Enable Flag|
Jump is a family of three-decle instructions that all map to the $0004 opcode and are represented as any of several different possible mnemonics, depending on the flags indicated in the second decle of the opcode. The opcode format breaks down as follows.
Format - Decle #1 Format - Decle #2 Format - Decle #3 0000:0000:0000:0100 0000:00rr:aaaa:aaff 0000:00aa:aaaa:aaaa
rr indicates the register into which to store the return address such that: rr == 00 indicates to store return address in register R4 rr == 01 indicates register R5 rr == 10 indicates register R6 rr == 11 indicates that the CP1610 should not store the return address, signaling a Jump without return
ff indicates how to affect the Interrupt (I) flag in the CP1610 such that: ff == 00 indicates not to affect the Interrupt flag ff == 01 indicates to set the Interrupt flag ff == 10 indicates to clear the Interrupt flag ff == 11 unknown opcode (behavior unknown!!)
aaaaaaaaaaaaaaaa indicates the address to where the CP1610 should Jump
Note that if the return address is stored in a register, the address stored in that register is the address that is exactly 3 addresses after the start of the Jump opcode, so that the subroutine will return to the next opcode after the Jump opcode. Some routines use the fact that R4 and R5 are incrementing counters, and so will place data after the Jump instruction. See Calling Conventions for more details on function calls.
The Jump opcode is often represented as many different mnemonics, to make life a little easier for the programmer. The mnemonic used to represent this opcode depends on the combination of the rr and ff parameters mentioned above, according to the following charts. Also, the instruction CALL label is an alias for JSR R5, label.
Mnemonics To Parameters
Parameters To Mnemonics
|rr == 00||rr == 01||rr == 10||rr == 11|
|ff == 00||JSR R4, $aaaa||JSR R5, $aaaa||JSR R6, $aaaa||J $aaaa|
|ff == 01||JSRE R4, $aaaa||JSRE R5, $aaaa||JSRE R6, $aaaa||JE $aaaa|
|ff == 10||JSRD R4, $aaaa||JSRD R5, $aaaa||JSRD R6, $aaaa||JD $aaaa|
|ff == 11||unknown opcodes|