Workspaces: ZP [BBC Micro disc version, Loader 3]

       Name: ZP                                                      [Show more]
       Type: Workspace
    Address: &0070 to &008B
   Category: Workspaces
    Summary: Important variables used by the loader
    Context: See this workspace in context in the source code
 References: This workspace is used as follows:
             * Elite loader (Part 1 of 3) calls ZP
             * LOAD calls ZP
             * MVBL calls ZP
             * MVPG calls ZP
             * OSBmod calls ZP
             * PIX calls ZP
             * PLL1 calls ZP
             * ROOT calls ZP


 ORG &0070

.ZP

 SKIP 2                 \ Stores addresses used for moving content around

.P

 SKIP 1                 \ Temporary storage, used in a number of places

.Q

 SKIP 1                 \ Temporary storage, used in a number of places

.YY

 SKIP 1                 \ Temporary storage, used in a number of places

.T

 SKIP 1                 \ Temporary storage, used in a number of places

.SC

 SKIP 1                 \ Screen address (low byte)
                        \
                        \ Elite draws on-screen by poking bytes directly into
                        \ screen memory, and SC(1 0) is typically set to the
                        \ address of the character block containing the pixel
                        \ we want to draw (see the deep dives on "Drawing
                        \ monochrome pixels in mode 4" and "Drawing colour
                        \ pixels in mode 5" for more details)

.SCH

 SKIP 1                 \ Screen address (high byte)

.CHKSM

 SKIP 2                 \ Used in the copy protection code

 ORG &008B

.DL

 SKIP 1                 \ Vertical sync flag
                        \
                        \ DL gets set to 30 every time we reach vertical sync on
                        \ the video system, which happens 50 times a second
                        \ (50Hz). The WSCAN routine uses this to pause until the
                        \ vertical sync, by setting DL to 0 and then monitoring
                        \ its value until it changes to 30