Difference between revisions of "Jump"

From Intellivision Wiki
Jump to: navigation, search
 
Line 29: Line 29:
 
<tr><td>ff == 10</td><td>JSRD R4, $aaaa</td><td>JSRD R5, $aaaa</td><td>JSRD R7, $aaaa</td><td>JD $aaaa</td></tr>
 
<tr><td>ff == 10</td><td>JSRD R4, $aaaa</td><td>JSRD R5, $aaaa</td><td>JSRD R7, $aaaa</td><td>JD $aaaa</td></tr>
 
<tr><td>ff == 11</td><td align=center colspan=4>invalid opcodes</td></tr>
 
<tr><td>ff == 11</td><td align=center colspan=4>invalid opcodes</td></tr>
</table
+
</table>

Revision as of 16:33, 11 January 2005


Jump is a three-decle opcode that is represented as one of several different possible mnemonics, depending on the flags indicated in the second byte of the opcode. The opcode breaks down as follows.

   Format - Byte #1     Format - Byte #2     Format - Byte #3
   0000:0000:0000:0100  0000:00rr:aaaa:aaff  0000:00aa:aaaa:aaaa
where:
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

This opcode is often represented as many different mnemonics, to make life a little easier for the programmer. The mnemonic used depends on the combination of the rr and ff parameters mentioned above, according to the following chart.

rr == 00rr == 01rr == 10rr == 11
ff == 00JSR R4, $aaaaJSR R5, $aaaaJSR R6, $aaaaJ $aaaa
ff == 01JSRE R4, $aaaaJSRE R5, $aaaaJSRE R6, $aaaaJE $aaaa
ff == 10JSRD R4, $aaaaJSRD R5, $aaaaJSRD R7, $aaaaJD $aaaa
ff == 11invalid opcodes